Come early or stay late and check out the waterfalls. The South Falls are just a few minutes walk from the picnic shelter. For a longer adventure, there are 9 more falls that you can hike to on the Trail of Ten Falls. There's also some great mountain biking and hiking in the park.
Bring your kiddos here!
There are lots of vineyards in the Willamette Valley and all are delicious, particularly if you enjoy Pinot Noir.
The Oregon Gardens are lovely during the summer! There's more than just the resort.
Come and soak in some natural (and clothing-optional) hot springs in the Oregon Cascades!
The Oregon Museum of Science and Industry is a great option if you're staying in Portland, particularly with kiddos.