The Krýsuvík area has a few geothermal fields which have solfataras and fumaroles scattered around them and these hot springs also have sulphur deposits which were mined in the past. Out on the reykjanes peninsula it is impossible not to be aware you are right on the mid Atlantic ridge since there signs of volcanic activity everywhere. Coming in to Keflavik International Airport the first thing to notice is the barren rugged lava fields drifting into the North Atlantic and the steam rise from the various geothermal areas including the world famous Blue Lagoon. The lava fields are of course the result of numerous eruptions occurring in the past and sometimes you can guess their age by the amount of vegetation growing on them. It takes a hundred years for one inch of moss to grow on lava so it is perhaps no wonder that these fields are quite stripped of vegetation. The fact is that even if there has not been an eruption here for around 700 years there are still plenty of earthquakes, and the fact that Reykjanes peninsula basically stretches out into the North Atlantic makes up for some rather harsh albeit periodical weather conditions.
Next to Krýsuvík is Lake Kleifarvatn which is the largest lake on the Reykjanes Peninsula around 8 km2. After an earthquake in 2000 the lake actually shrunk by almost 2 km2 and the theory is that some fissures must have opened up on the bottom absorbing water and causing this drainage. Some equipment was found on the exposed bottom of the lake which was later identified as instruments for spying of probably Soviet origin. This in turn inspired icelandic crime writer Arnaldur Indriðason to write the novel Kleifarvatn (The Draining Lake).
A little further down the road is Grænavatn Lake which formed in one of a few explosion craters formed by volcanic eruptions in the distant past, the lake has a vivid deep green colour. The lakes and the hot springs of Krýsuvík also referred to as Seltún are all within a few minutes drive of each other and are basically between Reykjavík and Keflavik International Airport. This means that going through this area can easily be combined with an airport transfer or a visit to The Blue Lagoon which is less than half an hour from here.
This area is also popular for northern lights tours since it is close to Reykjavík but has no electrical light pollution to speak of, so on a clear night this a good area to wait for aurora activity to appear high in the sky. The area also feels like a different planet so if you are planning to shoot your little sci-fi fantasy in Iceland this would be a definitive location to scout.