The Silfra Tectonic Fissure is a unique phenomenon on this planet. There are several other freshwater rifts similar to Silfra in Iceland, but Silfra itself is the most beautiful, interesting and easily accessible to recreational divers and snorkelers.
The visibility in Silfra exceeds 100m, making it some of the clearest water in the world, and divers and snorkellers dive and float between the American and Eurasian continental plates. There are even places where they can actually touch both continents at the same time.