#3 Whittier, Alaska
Almost all of the 200-plus inhabitants of Whittier, Alaska live inside a single 14-story building called Begich Towers. The rest live in their vehicles, boats, or another, similar building. Begich Towers was built in 1956. Back then, it served as an army barracks, but today, it is a town complete with a police station, post office, store, church, video rental shop, playground, and health center. They are all located inside the building.