The bathing area by night:
By night the inside of the restaurant gives the feel of a giant fish tank, but are you inside or outside it?
The pool is popular with both locals and tourists and bathers often spend several hours there, in and out of the water and inside the spa, getting treatments. The white mineral deposits are beneficial to the skin, especially for the treatment of psoriasis and eczema, and as a matter of fact they are used to produce skin-care products marketed under the Blue Lagoon trademark (and no, I'm not getting paid to tell you this).
The place is popular for promotional photography, especially for tourism and to illustrate magazine and newspaper articles about Iceland.
I don't know what this particular photo-shoot was for, but I got some nice shots of the photographer and the model:
Judging from the muscular look of the model, she is probably a fitness rather than a fashion or glamour model.
She seemed to be having a fine time despite the cool outside temperature, which was round 8 °C (this was in November).