At the deep end of Tokyo, there is a huge reservoir lake called OkTama (Okutama). And farther deep to the west of the lake, there is a floating bridge.
Once, there were small villages on both sides of the mountains. But about 70 years ago, the area was drowned to make a huge reservoir lake to provide drinking water for Tokyo people.
The two villages, though fortunately saved from being drown, lost contacts with each other. The mountains west of Tokyo are unbelievably steep, if not so high, and without bridges it is almost impossible to reach the village on the other side.
So, when the dam divided those villages, the authority made a temporal bridge by joining many rafts and keep them afloat with oil cans.
Since then, the floating bridge exists as it is, though the oil cans were replaced by plastic.
I made a nice soothing video. Enjoy!