Buildings You Need a Boat to Explore
No matter how much forethought you put into the construction of a building, there's no way to accurately predict everything that could happen to it. The building may be leveled by an earthquake, be hollowed out in a fire—or end up at the bottom of a lake.
Sometimes lakes appear after massive floods, and sometimes they are manmade by the construction of dams, creating underwater ghost towns. There isn't much that can be done with buildings left in the middle of the lake, unless you're a SCUBA diver or a boater. Then, abandoned buildings in the middle of a lake become things to explore.
The World Geography has a great piece featuring the stories of eight drowned buildings and gorgeous photos of each. Would you explore these buildings if you had the chance? I know I would.