Lake Reschen Italy, Since Roman times, the towns of Graun and Reschen high in the Alps near the Italian-Swiss border had been occupied. But in 1939, the local power company drew up plans for a dam that would give the area plenty of seasonal electricity -- but create an artificial lake that would unify two natural lakes and submerge the towns in the valley between them. Despite fierce resistance on the part of the villagers, the plan was eventually passed and the ancient towns submerged in 1950. (That pesky second World War delayed things a bit.) The settlement as it once was:
Today all that's visible above the waterline is the campanile, or bell tower, of Graun's 14th-century church tower. Below the waters of Lake Resia, the remains of 163 buildings house fish and eels instead of people, accessible only to divers. (Although I can't find any evidence that diving Lake Resia is actually allowed, which is unfortunate!)
When the lake freezes in winter, you can simply walk out to the bell tower. Local legend holds that on cold nights you can still hear its bells ringing -- although the bells were removed on July 18, 1950, a week before the waters came and drowned the church's bottom half.