Scott Mountain provides great views of surrounding mountains and a (very) distant peek of the Sawtooths on a clear day.
Silver City is a neat old mining town about two hours SW of Boise.
Deadwood is a great destination for adventure rides. It offers a multiple approach options, nice scenery, lots of camping options and can serve as a base camp for many side trips.
Squaw Butte is an easy half-day trip from Boise. It’s perfect for beginners, and provides an impressive view from the summit.