Sitting behind a volcanic ledge, right off the road to Landmannalaugar, hides an enormous crater. Hnausapollur erupted around 11,000 years ago, now it's filled with piercing blue turquoise water. Those in a 4WD can drive right up to the edge of the crater and peer into it from the car. It's also possible to carefully walk around the rim or obtain a permit (3500kr) from the Mountain Mall and go fishing in the lake below.
There's no road sign on the F208 pointing out this magnificent sight, which is around 200m from the road. Look for a dirt path leading up to a hill on the left before you reach Frostastaðavatn lake.