Blue Lagoon
Milky-blue geothermal waters in the middle of a lava field.
The Blue Lagoon is a geothermal spa located on the Reykjanes Peninsula, about 50 kilometers southwest of Reykjavik — and one of the most visited attractions in all of Iceland. The water gets its distinctive milky, opaque blue color from silica and sulfur minerals in the geothermal seawater, which is a byproduct of the nearby Svartsengi power plant. That industrial origin doesn't diminish the experience at all — if anything, the contrast between the raw black lava landscape surrounding it and the steaming turquoise water makes the whole scene feel genuinely otherworldly.
In practice, you spend your time wading through warm water (around 37–39°C) that stretches across a series of interconnected pools, some shallow enough to stand in, others deeper. The different packages give you access to things like silica mud masks (dispensed from buckets around the pool perimeter), algae face masks, and an in-water bar where you can order a smoothie or a drink without leaving the lagoon. The facilities are high-end — thick white robes, good locker rooms, a spa treatment menu if you want to book massages — and the whole complex includes a well-regarded restaurant called Lava Restaurant built right into the lava rock.
One important note: the Blue Lagoon sits closer to Keflavik International Airport than to Reykjavik, which makes it an ideal first or last stop on your Iceland trip. Many visitors stop here on arrival before the jet lag hits, or time a final soak before catching a flight home. Book well in advance — the Blue Lagoon uses timed entry slots and frequently sells out days or even weeks ahead, especially in peak summer and around the holiday season. Also worth knowing: the facility has faced temporary closures in recent years due to volcanic activity on the Reykjanes Peninsula, so check current status before you go.