The lagoon is located on the Reykjanes peninsula where you also find Keflavik international airport.
So for many it is either the first or last stop during a trip to Iceland. It is not necessary to visit it as part of a guided tour.
Just remember to buy your admission ticket in advance since the lagoon is often fully booked.
Same applies to lava restaurant the lagoon´s own restaurant.
Once you are soaking in the mineral rich waters there is only one thing to do:
Enjoy and relax floating in the waters of the blue lagoon. And of course applying the silica mud mask.