One of the most visited attractions in Iceland is the Blue Lagoon, or rather Blàa Lónið. Blue Lagoon is a geothermal spa located in a lava field in the southwest, not that far away from the international airport. The 37-39°C warm water is rich in minerals and good for people suffering skin diseases. The lagoon is not natural, it is water output from the nearby geothermal power plant. Considering it that way, you bath in expensive „residue/waste“ water.
Since it is that close to the international airport, many people drive there after landing or before leaving. From Reykjavik busses drive hourly, for example from the bus terminal BSÌ. The bus from Reykjavik costs around 20 Euro and is offered mostly by Reykjavik Excursion or rather FlyBus. However, other trip agencies, like Gray Line, offer trips to the spa too.
The standard ticket costs 6100 ISK online, which is around 50 Euro. However, there are options to use upgraded services too with extra towels or spa programs. The standard ticket includes the entrance and a silica mud mask. Drinks can be bought within the blue lagoon. Like literally, in the blue lagoon pond.
Blue Lagoon is one of the things you simply have to do while being in Iceland. It is just a typical tourist attraction. It is also quite expensive and depending on the point of view it might be not worth it. I enjoyed the trip very much and was grateful to be invited by a friend of mine. Even if is relatively expensive, I would recommend to see it at least once.