Blue Lagoon. So also for us. The weather was however not very good on Monday 3rd, so photos from the swimming bodies cannot be shown.
An image from outside the geothermal spa is the best I can deliver. As you see the lagoon is not as blue as the raincoat of my wife.
My friends at fru B told us to taste the "Svarti Daudi" when visiting Iceland. I did, and can agree that too much of that "Brennivin" is an extreme sport with high risk factor. The Viking beer however can be recommended.