We have been here many times and it is so relaxing to sit in the different hot springs and soak for a bit! It is also right along the San Juan River so if you get too warm, you can jump right in!
If you want to go on a hike, no matter the length, there are tons of scenic trails to be found. You can go on this website and adjust the distance, difficulty, and elevation gain to personalize your hiking experience and get recommendations.
There are a lot of places to go fishing as well, and there are stores where you can rent fishing gear to go out on the lake for a day.
There are so many shops on Main Street, tons of fantastic restaurants, parks, and a riverwalk to access the San Juan River. Sometimes wandering around downtown is the best way to explore a new place!