Twin Lakes was always a lightly fished lake. I always fished on the dam out there with rooster tails and would limit every time. This was when i was a kid and had no idea what i was doing
Depending on when you go in the summer, they could be thawed enough. Climbing Mt. Elbert is always a good story as it is the tallest in Colorado and a relatively easy hike. Probably a 5-6 mile round trip but nothing difficult anywhere on the hike
I used Noah's ark for rafting. It was a good group and nothing dangerous. Good experience if you aren't an adrenaline junkie
Leadville, 30m away is a cool town as well. Turquoise Lake is out there and will have bigger fish, but much more fishing priessure
Arkansas River (running along hwy between Buena Vista and Leadville) is decent fishing. Never caught anything big there, but good scenery