€45 entrance fee as of July 2015 if you book online.
You receive a bracelet with a chip at the reception which you use to lock your locker and to pay for drinks during the stay.
If you want to leave the Blue Lagoon for a bit ask at reception to let you keep your bracelet.
Adhere to the signs:
You have to leave your shoes shortly after entering.
You have to shower before you enter the water.
If you go to your locker again, you have to be dry immediately after the shower area.