Outside of Reykjavik, Iceland and the water is heated by the geo thermal springs and it's amazing! The lagoon itself is actually man-made with white concrete but the filtered water pumped in is from the springs. You also make a mask with the silt, it makes your skin feel great! You can buy a package and go straight from the airport (closer than the city) then make your return into Reykjavik. The cost is close to $90 per person for about 6 hours, there are restaurants there too and a hotel if you want to stay there, of course dressing rooms and showers