Swim in the lagoon.
Put the Silica Mud all over your body, but only use the one in the containers - it is clean and more hygienic.
Relax and float in the mineral waters.
Get up close to the wooden boxes as these are the vents where the hot water arrive, thus are the warmest parts of the pool.
Tuck yourself away in one of the caves, slip under the waterfall or enjoy the busy Steam baths.
There are lots of tour companies offering all inclusive package deals.
Reykjavik Excursions (http://www.re.is) and Iceland Excursions (http://www.icelandexcursi...) run all inclusive trips from Reykjavík. There are tickets available that make it possible to call in en-route between Keflavík Airport and Reykjavík, or vice versa.