Abandoned Michigan: Turtle Island
This little obscure, mostly-forgotten chunk of Michigania is smack on the border between Michigan and Ohio in Lake Erie (see the pic on the right). And since it's not far from Toledo, Ohio, the island's address is referred to as "Lake Erie, Toledo, Michigan."
After a mostly harmless skirmish between Michigan and Ohio in 1836 - referred to as the "Toledo War" - the island was attributed as Michigan property. Finally in 1973, the Supreme Court split the ownership between the two states.
Over the last 200+ years, the island was used for lighthouses and vacation homes, all of which have been abandoned and in ruins...but mostly trespassers visit the island looking for excitement on this forgotten, abandoned piece of land.
If you're thinking of boating over there, keep in mind, it's illegal to trespass, but you may be able to obtain permission from the owner.