The Blue Lagoon is a unique experience. The first thing that strikes you is the location. The BL is on the surface of the moon. Or so it seems as you are driven across the lava fields to get there. The logistics (done by Reykjavik excursions) are very good and make it quite easy to visit on the way to or from Keflavik airport, Iceland's main airport. Indeed I can recommend changing your trans-Atlantic itinerary to include a stopover in Iceland solely for the purpose of visiting the BL. Like most things in Iceland, the facility is well organized. While they do offer various treatments, the highlight is certainly the lagoon itself.

I strongly recommend visiting in winter to get the full experience of the land of fire and ice. Be advised, the minerals in the water will turn your hair into a salty matted mess that may take days to sort out, but it's worth it.