The Secret Lagoon is a great alternative if you cannot fork out the expensive price tag for Blue Lagoon. We weren't sure if we were ging to visit Blue Lagoon so we visited this lagoon first and after then visiting Blue Lagoon in the end, we can say that this lagoon comes nowhere near to Blue Lagoon.
However, it is budget-friendly, quiet and great spot to relax after visiting Kerlingarfjoell. We stayed here from midday until closing time and then went straight to our campground.