Asylum, deep sea, and deep space all take the cake. An Asylum because realistically there might be insane people who have developed homesickness for their prison. You don't want to stumble upon somebody who will eat your face while screaming [u][i][b]"OH DR. KENNETH HOW I MISS YOUR RELAXING MEDICINES!!!"[/b][/i][/u] Plus Arkham Asylum and HP Lovecraft make them sound spookie. The deep sea because realistically because weird -blam!-ing things like yeti crabs, those fish with light bulbs sticking out of their heads, and colossal squids exist. Human vessels aren't even strong enough to withstand such pressure. Also unknown beings like Cthulhu and the Kraken. [spoiler]ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn [/spoiler] and deep space because aliens and other dimensions and weird shit nobody knows about