There are a few parks that still offer solitude and the outdoor exploration experience. I won't say which, but we camped for extended times in the last couple of years at two of the parks near the top of the list. You just have to be willing get out and walk -- most park visitors are not willing to do much of that, unless it is on a very well marked, publicized trail. At one very popular park, we had a park enforcement ranger ask if that was us he saw parked near a little used trailhead, which we affirmed. He said that was one of most underappreciated gems in the park. We agreed, having lost count of the dozens of different wildflowers we had seen on that obscure trail. And then there are the national monuments and National Park adjacent areas. Often I am bewildered why some areas got left out of a nearby park -- certainly not due to the lack of great scenery and hikes.
It is out there -- if you look hard enough.