A big part of Europe's allure is its historic architecture that continues to stand the test of time. Ancient castles, fortresses and palaces are truly the stuff of fairytales, but sometimes, those tales don't have happy endings.

In fact, several of Europe's historic hotels have horror stories sprinkled into their very foundation.

So, as you fall asleep in a castle, you may expect to hear a few bumps in the night — and not just because they're old and creaky — but because these notoriously haunted properties have some unwelcome guests that simply refuse to leave.

The 31-room Mermaid Inn has been welcoming guests since 1420. Located in East Sussex in the town of Rye, the inn's cellars go back even further — to 1156.

Here, you will find a Tudor exterior, creaking floorboards, sloping ceilings and secret passageways that were used by smugglers in the 1700s.

As you might expect, lots can happen in an inn and pub over the course of 600 years. People can get married. Celebrate a birthday. Make new friends. Die.

Guests and workers of the Rye, England, inn have reported numerous haunts. From seeing a self-rocking rocking chair to a ghost that walks through walls to a well-clothed gentleman sitting at the end of beds, the stories are rampant. 

Overlooking St. Stephan's Green in Dublin, the iconic Shelbourne is an aristocratic hotel that has welcomed royalty, celebrities and politicians.

In fact, the Irish Constitution was drafted in Room 112 in 1922. The five-star property features 265 bedrooms and remains the talk of the town in more ways than one.

Just because you're a luxury hotel in the heart of cosmopolitan Dublin doesn't mean you cannot experience a haunting.

The property's most famous ghost is Mary Masters, a little girl said to have died of cholera at the hotel in 1846. Guests have reported hearing her cry and feeling her climb into bed with them at night.

Set on 12 acres of Welsh gardens and woodlands, Roch Castle has been a part of history since it was erected in the 12th century.

The home of families from the royal court for generations, the property was converted into a six-bedroom luxury hotel in 2008.

King Charles II had many loves, including his first mistress, Lucy Walter, who was born in this castle. Lucy bore the king's son, the Duke of Monmouth, before she died at a young age.

Reports of her ghost have been spotted around the castle, with her wearing a long white dress that flows as she moves. But don't stand in her way, she'll just walk through a closed door to escape you.

So luxurious is this Danish castle found in Zealand that its onsite restaurant, Nordic, has a Michelin star. Guests can enjoy one of 34 rooms during a romantic and gourmet stay.

The Relais & Chateaux property is one of Denmark's oldest castles, and it has sat overlooking the Odsherred peninsula land for more than 800 years. The property is the only one granted Geopark status in Denmark by UNESCO.

One or two spirits are not enough for this Danish hotel, which is said to be haunted by 100 spirits!

The most notorious of them is the White Lady, a ghost of a girl who was promised by her father to marry a nobleman. As tragic love stories often go, she was already in love with another man and pregnant. It is said she was entombed inside the castle's wall by her enraged father.

In 1910, during renovations to the castle, workers discovered the remains of a woman in a white dress within the walls.

Just 8 miles outside of Edinburgh awaits the stately Dalhousie Castle Hotel, which has stood in this very spot for 800 years.

Scotland's oldest inhabited castle, once the ancestral home of the Ramsay Clan, welcomed guests such as Sir Walter Scott, King Edward I, Oliver Cromwell and Queen Victoria.

Today, it serves as a four-star hotel featuring a network of passageways and a dungeon that you can visit during your stay.

Another love story gone wrong occurred at Dalhousie Castle when 16-year-old Lady Catherine was forbidden by her parents to see the man she loved, a stable boy for the family.

So anguished was she that she refused to eat and starved herself to death while she was banished to the castle tower. It is said you can still hear her wailing during the night.

Known as the Grey Lady due to sightings of a girl in a grey dress with puffy sleeves, she has been spotted frequently and has even been captured in photographs at weddings.

Part of the global Clarion budget hotel chain, you would think the Hotel Bilan doesn't offer the same ambiance and history as others on this list.

However, the Karlstad building is actually one of the city's most famous, as it was formerly a prison built in the 1800s. It operated as such for nearly a century, hosting some of Sweden's biggest criminals.

A former prison is bound to have some tales, and that is certainly the case for Hotel Bilan.

During the 1860s, a priest named Anders Lindback was an inmate sentenced to death for lacing the communion wine with arsenic and poisoning his congregation. Before he could meet the executioner, the priest hung himself.

Now that the basement of the hotel has been converted into a museum of the prison, it seems the priest likes to hang around and has been said to play tricks on the staff.

Within the bustling city of Rome, the medieval Castello della Caselluccia stands surrounded by its gardens and green space.

The four-star property outfits its rooms in antique furnishings in a space filled with wooden-beam ceilings, marble bathrooms, vintage flooring and Italian frescoes. Bella!

With more than 1,000 years of history, it's no surprise Castello della Caselluccia is haunted. Its ghosts, however, include the ghosts of horses seen galloping in the distance!

One unlucky spirit was struck by lightning in the castle tower, and people swear they can feel his presence. (Is it electricity?)

Nearby, Rome's Emperor Nero is buried, but it is said his grave is too cold and that he prefers the warmth of the castle instead.

A medieval castle overlooking the small town of Cardona, Parador Cardona is a gothic property with panoramic views.

Fortified in the ninth century, the hotel features towers, fosses and other elements of architecture that give its guests a sense they have traveled back through time.

With the amazing views from these hotel rooms, we understand why some guests would never want to leave.

That seems to especially be the case in Room 712, where the furniture finds its way to the center of the room every night.

Known as the fairytale hotel due to its construction that mimics the Viking and Nordic architecture of ancient times, the Dalen Hotel has been in operation since 1894.

Monarchs have passed through the doors of this charming hotel that is surrounded by Norway's famous fjords.

The hotel's longest guest is such a regular that the staff sets a place for her at the dinner table. Miss Greenfield of England visited the property veiled in secrecy. You see, she was unwed yet carrying child. She delivered during her stay in Room 17 and returned to England ... without her baby.

The staff found the dead newborn in the room, and Greenfield was charged with murder and set to face trial. She committed suicide instead, and back in Norway, guests have felt her presence ever since.

Others have heard the cries of a baby as well.

This "tallest castle in France" dates back to the 11th century and was once the home of a future king, Henry IV.

The seven-story, 204-room castle is home to the Duke of Brissac, but three of its rooms are available as a bed and breakfast.

Whether you enjoy an overnight in a suite or choose to visit for the day, you can explore the 170-acre property filled with gardens along the Aubance River.

The chateau is filled with stories of lust, love, revenge and even murder during its 10 centuries in the French countryside.

One unlucky victim is la Dame Verte, the Green Lady, who continues to walk the halls of the chateau.

You see, she was having an affair, which triggered her jealous and angry husband into such a fit of rage that he killed her when he found out. She's forever trapped within the chateau.

For another unusual lodging option in Europe, the Karosta Prison welcomes overnight guests — all with the freedom to come and go as they please.

You'll actually have the opportunity to sleep in a former cell for just 15 euro a night and even receive the "full inmate experience," complete with prison guards who will put you through the ringer.

The prison, built at the start of the 20th century, was used as a military prison by both Soviet and Nazi leaders. Most prisoners here didn't walk out alive, having been sentenced to death and shot.

With so much pain taking place, it's no wonder the place is haunted. The echos of chains can be heard moving throughout the halls, cell doors slam shut or mysteriously open, and light bulbs unscrew themselves — all seem to say "get out," if you ask us.

An old-fashioned property where time looks to have stood still since the mid-1800s but is fully enriched by modern comforts and conveniences, the Toftaholm Hherrgard is a tranquil sanctuary found on Lake Vidostern.

Forty-four rooms are available in the classic manor home that was built by Swedish nobility and you can sample a bit of manor-house life with a visit.

It's not just women who mourn lost love into the afterlife.

Here, the daughter of the baron who owned Toftaholm Hherrgard was set to marry a man chosen by her father. She, too, loved a peasant boy, and on the morning of her wedding, he hung himself in what is now Room 324.

He never left.

Stay within one of the numerous apartments of Chillingham Castle, and you will feel like royalty.

Originally a 12th-century monastery, the castle became a stopping point for King Edward I, as it lies on the border of England and Scotland. Owned for 800 centuries by the Grey family, it was left abandoned for 50 years before the Wakefields purchased and renovated the castle, breathing into it new life.

Fully embracing its legendary status as one of the most haunted hotels in England, Chillingham Castle practically dares you to spend the night.

Even the world-renowned poet Henry Wadsworth Longfellow wrote about Chillingham Castle and its "chilling" haunts.

There are four ghosts making their presence known: the ghostly White Pantry lady, the creepy feeling ghost found in the Chamber, the voices of the ghosts heard inside the chapel and the shadowy ghosts of the courtyard. Basically, good luck finding any place for solitude throughout this property.

Within Killarney National Park is the ancestral home of Clan O'Donoghue's chief before falling to the Brits and becoming the home of the Earls of Kenmare. 

The 16th-century tower has three rooms that are available for overnight experiences at the castle, and additional bookings can be made at the property's cottage and Quarry House.

Looming over Leane Lake, it is said O'Donoghue slumbers beneath the waters of the lake before waking and circling the lake on a white horse every first morning of May, every seven years.

This isn't an evil haunting, though — finally! Those who catch sight of him are said to have good fortune bestowed upon them for the rest of their lives.

In Northern Wales, you'll find this charming castle that was constructed in the 1200s.

The home of the Grey family, Ruthin Castle played a role in U.K. history, including a siege during the English Civil War, where Oliver Cromwell's army demolished the castle in 1646.

Transformed into a hotel in the 1960s, Prince Charles stayed here before he was invested as the Prince of Wales.

Here's another gray lady who is spotted at night roaming the halls of an ancient castle.

This Lady Gray caught her husband having an affair, murdered his mistress and was sentenced to death. She continues to haunt the property, which happens to have its own torture dungeon.

Nestled along the famed Loch Ness of Scotland's Highlands, this Victorian home provides a cozy stay in one of the most picturesque destinations of the U.K.

Eight individually styled rooms are available to book singularly or as the entire property for guest events.

It's not the mythical Loch Ness Monster that lends mystery to Foyers Lodge. Instead, it's the doings of the property's former owner, Led Zepplin's Jimmy Plant and occultist Aleister Crowley.

Crowley is said to have attempted to raise the dead around the property, with so much success that there are rumors of more than 100 spirits surrounding Foyers.

That includes the ghost of a small dog seen within the home.

This cool hotel is situated within the walls of an 18th-century Arabian fortress. Overlooking the Andalusian countryside from its hilly perch, Parador de Jaén is monumental.

Of course, with its location comes some amazingly fresh produce used in the hotel's Spanish restaurants.

Multiple rooms have their share of ghost stories at Parador de Jaén, including Room 22. Here, another brokenhearted woman cries in the night, waking guests from their slumbers.

A prisoner nicknamed Terrible Lizard was locked up in the fortress and died of hunger. He still wanders the halls to this day, perhaps searching for something to eat?

Along the Rhine River in Germany are numerous castles to be explored. You can actually stay in the former Reichenstein Castle, the ancestral home to the Barons of the Kirsch-Puricelli family. 

The castle goes back to the 11th century and overlooks the river with a museum on property dedicated to its ancestral past.

The lord of Reichstein Castle in the 16th century, Dietrich von Hohenfels, and his nine sons were ordered to be hanged here by the Holy Roman Emperor Rudolph von Hapsburg for robbery.

In an effort to save his sons, the man asked the executioner to chop off his head and allow his sons to live if his body managed to walk past each son before falling down. It worked, and his sons were spared!

Now, his headless body continues to walk around the castle as a ghost.

A UNESCO World Heritage Site, the 15th-century Chateau de Marcay was built on the ruins of an 11th-century fortress.

A hotel since 1973, its rooms offer views of the grand garden estate set in the Loire Valley.

Not only has a ghostly woman in a white dress been spotted in the chateau by guests, but the legend also has it that she's actually a werewolf.

A lady of the house, she apparently transformed during one full moon, and a farmer shot her dead.

She resumed her human form and walks the hallways to this day.

For more than 150 years, the best and brightest of the world have stayed at the tony Langham in London, considered to be Europe's first "Grand Hotel."

Nearly 400 rooms, suites and residences and high-end dining are treats to those who stay at the Regent Street property within steps of Mayfair and Covent Garden.

While there are guests The Langham has proudly hosted, including Winston Churchill, Oscar Wilde and Mark Twain, there are quite a few it could do without.

That includes Emperor Napoleon III, who spent much of exile here and must have enjoyed it because his ghost remains. Or there's the German prince who jumped out of a window. When he is present, a chill is in the air.

And Room 333 is said to be the worst of all the haunted spaces. Here, a honeymooning doctor murdered his wife and then killed himself. People have felt his evil presence and even spotted an apparition in this room.