Ever wondered what it takes to get into Fort Knox? Fancied a peek inside the Coca-Cola Safety Deposit Box? Would you dare to visit Three Mile Island? <br><br> The world is full of secret places that we either don’t know about, or couldn’t visit even if we wanted to. Now you can glimpse the Tora Bora caves in Afghanistan, visit the Tucson Titan Missile Site, tour the Vatican Archives, or see the Chapel of the Ark. This fascinating guide book takes a look at 100 places around the world that are either so hard to reach, so closely guarded, or so secret that they are virtually impossible to visit any other way.