Staying in Portland, we rented a car and took a day trip to do the Mt. Hood Scenic Loop. I definitely recommend it. Mt. Hood is so majestic and the trip along the Columbia River Gorge is really beautiful. Close to the Village of Government Camp we stopped at a trail head for Mirror Lake and took a nice hike to the lake -- around 3 miles altogether. To be completely legal and make a contribution to the upkeep of the great facilities, we bought the $5 Park Day Pass at the visitor center in town. The hike wasn't too hard -- lots of kids and people with dogs on the path -- but the path climbs the whole way up. The path was very scenic and once at the Lake itself, on a clear day you see Mt. Hood and its reflection from the far side.
Going along the Columbia River Valley, I recommend driving on the Washington side if you have time (route 14), especially the stretch between Hood River and Cascade Locks. It is a little slower but the roads are still very good and the views are amazing, with Mt. Hood in the background.
If you own or manage Mount Hood, register now for free tools to enhance your listing, attract new reviews, and respond to reviewers.