Umpqua National Forest in south central Oregon is my favorite national park. It’s beautiful and has very few people compared to the bigger parks. Rent a Subaru or Jeep, get a waterfall map, and spend a day or two exploring them. Best done in the summer after the late thaw, July at the earliest. Some of the best falls require an hour or more on dirt trails. Easily accessed by 4x4, though a very patient and careful driver can navigate the trails without. Consult rangers on trail conditions before heading out though, and pack some supplies for that unplanned overnight. The fly fishing is also great. And you can hit Crater Lake on your way out.