Did some swimmin and soaking over at Meadow Hot Spring south of Fillmore UT off Interstate 15. There are 3 hot spring pools in the area, two of them are soakable and the third is more like a fish pond. One of the pools is 40+ feet deep and scuba divers bring in their gear and explore the depths. There is a rope right above the deep section so one can sit down and not fall to the bottom. Temp was around 100 degrees when we visited.
Melissa and I got in at night and camped right next to the fish pond, we walked over to the warmest spring and soaked alone for a few hours before two dudes and a chick walked in. We all soaked nude regardless of the warning sign and talked about dumb shit for an hour before one of the dudes and the chick started pumping. Apparently the man was married, but not to the woman he was cram-jamming. It was kinda gross so we got out and went back to the tent for the night. We got up early the next day and had the whole place to ourselves for a few hours. We soaked, swam, drank beers and eventually porked before a family showed up. They picked up the trash they left the day before and looked for some jewelry that they lost. Melissa ended up finding it in the pool under some sand. They were hella stoked.
Directions: Heading north on I15, take the 133 south in the town of Meadow. You will pass a Chevron station on the right, keep going south for 1.4 miles to a graded dirt road on the right. This road will take you west back over the 15. Stay on this road heading west until you get to the parking area on the left. The spring is located about 150 yards from the parking area. Here are directions from Google Maps: http://goo.gl/maps/fpqeu