Comment by mcswell

Iceland has the Þingvellir valley, which is an above-sea continuation of the rift valley down the middle of the Mid-Atlantic ridge. It includes the Silfra, which is underwater (fresh water) at the lowest part of the valley. The Great Crack in Hawai'i is of course not such a major rift, but it is the same idea: upwelling magma raises the ground, creating a crack like in a loaf of raising bread.

The Great Rift in Idaho is another volcanic rift valley, which (IIUC) passes through Craters of the Moon National Monument (where the Apollo astronauts trained).