Really unique place. The volcanic hot springs are, of course, hot. Very relaxing. We walked around on a sunday but didn't take in the springs till Monday. It was a lot less crowded on Monday. Wife had an amazing expereince in the spa -- a bit pricey but worth it. The breakfast was outstanding. The buffet down at the springs, while very good, was a bit pricey. So was the breakfast, but it was included in our rate so no complaints. Stuff is more expensive here, but that is not unlike other resorts around the world (i.e. 4 or 5$ for a diet coke at the bar).
But, you are here to see the volcano (not much going on with it now, which was a shame, but still impressive) and to go to the springs. So nice and relaxing. Unlike anything I've seen. Go do it.
Had our 5 y/o with us and he enjoyed too. Turndown service and attention to detail good too.