Tumalo Falls hike comes highly recommended. Also, orienteering at Dutchman Flats, obviously.
Smith Rock if it isn't super-duper hot/sunny: not that much shade. Lava tube cave on the other hand, is great if it is super-duper hot/sunny, it's always some cool temperature (bring a sweater!).
Hike up South Sister from Devil's Lake trailhead. There's a mini crater lake on top that is almost as cool as the "real" crater lake.
Not really up to proper hikes any more - especially not in the heat! We may head out early to Smith Rock and do a little before the heat of the day.