Arizona Ghost Town...one of my favorite memories is taking a cross country road trip with my (much older) boyfriend and jumping out of the Jeep and having him yell at me- "don't run through the cactuses!!!!" it cracked me up.
Battleship island in Japan. The entire island housed 3x what it should have, and managed it by putting them in obscenely crowded apartments like this. Now, the entire island is abandoned, and is restricted to the public. These derelict sky-scraping ghettos fall without an ear to hear them.