After you hike the very very steep trail up to the lookout point you can hike back down and swim in the lagoons. They are not hot springs but were very refreshing considering how hot it was. Its such an unbelievably tranquil setting. I don't watch LOST but someone in our group said it felt like we were there.
Here is a pic of where the water flows out from underneath the lagoons. If you look to the top of those small waterfalls, that is where the lagoons sit.
Earlier in the day a guide led us into a cave by candlelight. We swam through the cave and climbed up along side waterfalls inside. We also got to jump off a small cliff into some not so deep water. It wasn't nearly as high as the cliff in San Marcos but it was inside a cave which made it pretty fun. Oh and we also jumped off a 10 Meter high bridge inbetween the cave and Semuc but when you can jump straight off the bridge, its nowhere near as scary as having to jump out from a cliff. I'm getting pretty good at jumping from high places. I wonder what I'll find next!