Amazing views from Trinity Mountain
The Boise National Forest has over 2 millions acres of pristine northwest wilderness full of pine forest, mountains, streams, and lots of wildlife like elks, bears, deer, and coyotes. As I said, the park is huge, so you should be a little bit of investigation before you go and decide what you want to see and do...after all, Boise National Forest has over 200 lakes, 500 hiking trails, and dozens of campsites.
Personally, I'd suggest driving up to the Trinity Mountain Recreation Area, the highest point in the national forest. Once you get there, you can make a short hike to the Trinity Mountain lookout (over 9,000 feet above sea level) and lake in one of the most spectacular views in Idaho. If you go after the snow melts, the alpine lakes will be full and the whole place will be covered in wildflowers.