Here is a quote from wikipedia:
......as well as the special tectonic and volcanic environment. The continental drift can be clearly seen in the cracks or faults which are traversing the region, the biggest one, Almannagjá, being a veritable canyon. This causes also the often measurable earthquakes in the area.
Some of the rifts are full of surprisingly clear water.
One, Nikulásargjá, is better known as Peningagjá ('penny canyon'), as it is littered with coins at its bottom.
Throw in a coin, make a wish, and watch the coin carefully; legend has it that if you can see your coin hit the bottom it will come true.
-K