Secret Lagoon (Gamla Laugin) is the oldest swimming pool in Iceland, originally built in 1891 in the geothermal area near Flúðir. The lagoon is fed entirely by nearby hot springs and even a small active geyser that erupts every few minutes.

The water stays naturally warm year-round (around 100 - 104°F) and constantly refreshes itself, giving the pool a clean, simple feel. Compared to places like the Blue Lagoon, Secret Lagoon is much more low-key and traditional, making it a great stop if you want a more classic hot spring experience.

You can rent a towel and swimsuit here, up-to-date prices are listed on their website :)