Laugarvatn
If you don’t like crowds, Lake Laugarvatn is a great alternative to the Blue Lagoon in Iceland. Plus you won’t have to sell a kidney to enter. “Swimming” in the lake, which is about 100 degrees, is free. I was the only one there a little before 9 a.m. when I took this photo. I came back after noon, and there still wasn’t more than a dozen people in the lake. Most were in kayaks.
The Fontana Spa is a number of pools connected to the lake. They aren’t free, but they are only about half the price of the Blue Lagoon and are likely to be far less crowded.