Yup, Cascade rafters is a good choice, BUT, getting there might be a challenge. There IS tubing on the Boise river, which is much tamer, but more easily accessible, AND a fairly lazy activity!

They're not running a Shakespeare play that night, but the Idaho Shakespeare festival is a GREAT way to spend an evening -- www.idahoshakespeare.org.

Also, a stroll along the Greenbelt is a nice way to start the day -- look out for the bikes! (not that it's fun to ride on, you'll see LOTS of wicked tree roots!)

the 25th is a Saturday, and there's a neat "farmer's market" downtown in the morning -- a wide assortment of foods, art/crafts, performances -- it's pretty cool!