▲As he opened the door, he found a soundproofed room covered in plastic, as well as a suitcase in the middle. Inside the suitcase were jewelry and tapes with the messages "Save yourself" and "No No No" written on them.

▲Singer Castle was built in 1896 by Commodore Frederick G. Bourne. It's located on Dark Island, New York.

▲They found a bed inside. But the twisted thing is that the bed was way too big to have fit in through the small door. Implying that the house may have been built around the room—and whoever was staying in it.

▲When the original owner died, the new owners discovered a number of secret passageways, and even a dungeon in the castle!

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In 2010, a room completely untouched for over 70 years was found in Paris. The apartment belonged to Solange Beaugiron, who left the city before WWII started, never to return.

▲A Redditor reported that two friends bought an old farmhouse and found a secret door in a closet. And if that wasn't weird enough, the door was only a few feet tall.

▲Years ago, a Redditor posted photos of a crawl space in the attic of his new home, where he found a door with a padlock.

▲H. H. Holmes reportedly killed all the workers who built the hotel so no one would know what the construction actually looked like.

▲This Chicago hotel was built by serial killer H. H. Holmes. It featured secret rooms, passageways, trapdoors, chutes, and a dungeon of acid vats and quicklime.

▲They discovered that someone was actually living there and not paying rent. They ended up changing the locks and left a note to the squatter about getting his or her belongings.

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A couple from Shropshire, England found a metal grill in the hallway of their new farmhouse. They decided to open it and check where it led to.

They found what looked like an old chapel, with a wooden cross on the floor, hooks on the ceiling, and a wooden pew. This was supposedly a hidden place for persecuted Christians to practice their religion.

▲Inside they found a heating system, food, wine, and phone lines. The remains of a goat were also found. The animal was probably their source of fresh milk.

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They found a small place in the attic. It looked like it was used by people hiding from the Nazis, potentially Jews. There was an old map of Britain, with supposedly safe locations marked on it.

▲Placer High School in Auburn, California was being renovated when workers came across a secret room. The room was a shelter built during the Cold War. There was food, water, medical kits, and even radiation suits inside.

▲In 2016, a woman in Pennsylvania discovered a secret room in her basement.

▲A family was doing renovations in their newly-bought house when they found a passageway behind a bookshelf that led to a room.

▲An Imgur user posted a number of photos of a spiral staircase he found behind a bookshelf in his house.

▲In 2000, books started to go missing in this 1,300-year-old abbey in France. All kinds of security measures were put in place, yet books were still disappearing.

▲Apparently the culprit was a professor named Stanislas Gosse, who discovered a secret entrance and was taking the books to his apartment.

▲Inside, there was a note from the previous owner saying that the house had a serious mold problem, and that the mold made his children very sick so they had to move out.

▲She eventually discovered that the house was previously owned by an abolitionist sympathizer, so the room was most likely part of the Underground Railroad. This was a network of secret routes and safe houses for slaves to escape.

▲Downstairs, he found candy, a blanket, keys, and a few dolls. It looked like someone was actually living there!

▲Students at Ohio State University made a surprising discovery. The door in the back of their cupboard didn't lead to a maintenance room, but to a basement instead.

▲While building a road in 2010, French engineers found a WWI German trench room.

▲A construction worker was renovating a bathroom when he found something strange after taking down a wall.

▲A group of students decided to rent a house in Norway. At the time, the landlord told them there were rumors of a secret room, so they decided to look for it.

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A portrait of Madame Marthe de Florian (the owner's grandmother) by painter Giovanni Boldini was found in the apartment. It's worth US$3.4 million!

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Surely you've seen it in movies: the bookshelf that's actually a door, or the attic that hides a secret room. In this gallery, however, you'll find real-life examples of secret rooms that have been discovered. Some of these are really creepy! Take a look.

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He found an office with a two-way mirror looking into the guest bathroom. Creepy!