From priceless treasure found inside a lost city, to an ancient manuscript hidden behind a wall, we explore mysterious secrets lost deep inside various unseen chambers, like tunnels, caves, or even burial sites.

From clandestine nuclear weapons programs to a secret Cold War bunker hidden in the mountains, or even World War 2 technology at the bottom of the sea, we explore the unlikely people, and surprising places behind the discoveries of the most top-secret information.

From ancient religious texts buried in Egypt to cultural relics found at sea, or even a tower of skulls hiding under the earth, these lost artifacts change what is known about certain sacred beliefs.

From a deadly discovery hiding under one of America's most loved national parks, to a Nazi era weapon sunk off the coast of New Jersey, you never know where a killer find is hiding or who may stumble upon it.