The Blue Lagoon spa, which is near Keflavík, was apparently created accidentally when the nearby geothermal power station (above) discharged excess heated and supermineralized seawater onto the lava fields. It's heavily promoted to the tourists, so I was a bit wary, but it was very nice. The water is warm-to-hot, salty, completely opaque with minerals and algae, and the bottom of the lagoon has a nice squishy/gravelly texture. There's silica mud to play with (it's supposed to be good for your skin). You can enter directly from indoors and pass through a door to the outdoors already safely ensconced in the warm water. It's easy to just lie back and forget the world exists. Until the military-precision every 2 minute take-offs of the next Icelandair departure bank pass overhead. Though that only lasted about 20 minutes at most.