Idaho is famous for its whitewater rafting. Not being a very adept rafter myself, I prefer to go with a guide. It would be a shame to live near all this great rafting and not partake of it, so I make sure that at least once a year we take a half day trip on the lower South Fork of the Payette River. It's 45 minutes from Boise to Cascade Raft and Kayak. There, for $50, you can have a guide take you and your party (and maybe a few others) down the river.
The South Fork has class III and class IV rapids, but they are not too daunting for novices if you are able to operate a paddle. It might be too frightening for senior citizens unless they are very fit, but generally I think most people could do it fine. If in doubt, call and ask one of the local rafting companies that does that stretch of the river.
Recently there was a tragic death of a veteran guide on this stretch of the river, in a class IV rapid called the Staircase. I've done that rapid several times, including this past week, and I couldn't help but think about him. At least he died doing what he loved...but I wonder if the crew didn't paddle as instructed and flipped the raft, or what went wrong. Apparently he got trapped in rocks and drowned before he could be rescued. Many, many tragedies happen in all walks of life though - don't let this one deter you from this stretch of the river. That guide died doing what he loved and he loved it for a reason - rafting is exhilarating and the scenery is gorgeous.
Another nice thing about Boise is that you can float the Boise River on your own raft or inner tube without a guide on hot days. You go to Barber Park and then float down to a take out in Ann Morrison Park. It is a great way to spend a few hours and I hope to squeeze it in this year before it's too late.