I think Retreat is definitely a one night stop over, and think it's the ONLY way to experience the Blue Lagoon. If you stay 2 must get full suite but I thought one night just right. Until we heard this hotel was opening, we planned to skip the Lagoon as too crowded, but we really enjoyed it for one night. It was t a place I'd be rushing back to, but really enjoyed being able to experience something famous in Iceland without the crowds.

Tonight in Reykjavik we had dinner at the Michelin one star restaurant, Dill, and thought Moss at the retreat at Blue Lagoon was better. Now we are not expecting San Francisco ( where we live), Paris or
London, Tokyo high end restaurants as it's Iceland! But for here we thought Moss pretty darn good. Better than expected and Dill quite frankly was a bit of a disappointment. So far really loving Tower Suites. Not for everyone, but views amazing and I didn't see anything close in downtown Reykjavik. I'll write it up later when we leave but so far very happy. Again not for everyone no restaurant ( they do have breakfast and can arrange catering for dinner, etc) , no gym, no Spa etc, but 5 star rooms and views.( have to get the right rooms - 2 out of 7). Did not see anything close in downtown.