The Silfra fissure is the only place where you can dive directly in the crack between the North American and Eurasian continental plates (which are drifting apart about 2cm per year).
The underwater visibility in the Silfra fissure is over 300 feet, which creates an underwater experience that will rarely, if ever, be surpassed.
But it's cold! Water temperatures are between 35°-39°F. Drysuit diving, for sure!