Skiing. Sun Valley is a big ski resort there.
Hiking and mountain biking would probably be big pursuits as well. I would imagine that kayaking or canoeing is something with good opportunities there.
Hunting and fishing are probably good if you're into either of those.
If you have a good telescope, there are probably good spots for stargazing, due to very low levels of light pollution.
Pray to get out of there?
Pay a visit to some of those terrific Ida HOES!
Peel em,fry em & share!
Go to the library and browse...
probably depends on what you're doing in Idaho, in the first place