This place is not well known but it's well worth a visit! By the beach in a tiny town called Hauganes there are three hot tubs and a boat hot tub. There are small changing rooms on site but keep in mind that this is not a spa, every thing is very basic.
A few steps from the tubs you're in the ocean so you can take a dip before warming up in the hot tubs. Views are great and overall I highly recommend this place.