First caveats: I'm 59 and only do easy hikes, 2 miles or less. So there are lots to do in each park that I didn't attempt.
It is hard to rank the parks as they were all so different from each other. But I'll try.
1. Crater Lake. WOW this is one you have to see to believe. The lake is so blue. You need to drive all around the lake to see it from the different views. I did 1.5 days here. If you wanted to do some of the longer hikes or take the boat tour, 2-3 days would be good. Note: if you want to go to the lake, they are closing the one trail to the lake in 2025 for maintenance and rebuild the boat dock. Expected to open in 2026. Highlights:
- Rim - it is paved around the lake at Rim Village. Great walk. See the lodge if you are interested in Parkitecture.
- Sun Notch - easy hike with amazing views of Phantom Ship
- Godfrey Glen - easy hike through old-growth forest
- Castle Crest - would be an even better hike in the summer with the wildflowers but I still liked it.
- Lady of the Woods - nature hike near Steel Visitor Center
- Pinnacles - different side of Crater Lake showing remnants of the volcanic activity
- Plaikni Falls - 2 miles to a waterfall.
2. Redwoods. WOW again - big, big trees. I only did the central and northern sections of Redwoods due to travel time. 2 full days Hikes/stops:
- Fern Canyon - Normally need a reservation during busy season. Davidson Road to get there is an adventure in itself - narrow, windy, gravel and small stream crossings. Saw sedans to pickup trucks making the trip fine. The hike is across streams as well.
- Gold Bluff Beach - not a hike, just a stop on the same road as Fern Canyon.
- Lady Bird Johnson Grove - easy hike through nice grove of redwoods
- HWY 101 - stopped at several overlooks. Interesting Redwoods NP goes out into the ocean to protect marine life.
- Klamath Beach drive to overlook
- Crescent Beach
- Stout Grove - easy hike through nice grove of big redwoods
- Newton B Drury parkway - scenic drive. Some hikes off this including Big Tree Wayside (1500 year old tree).
3. Yosemite. I am surprised it wasn't higher on my list. If I had to do again, I would have gone earlier in the year. I didn't realize that Yosemite Falls is not a year round fall. By September, it is dry. 3 days Highlights:
- Mariposa Grove. Since I skipped Sequoia NP, I was glad I could see sequoias here.
- Glacier Point - scenic drive with overlooks at Washburn Point and Glacier Point. There are also popular hikes here but I didn't do those.
- Valley
- Tunnel View
- Bridal Veil Falls. Walk to one of the few year round waterfalls
- Vernal Falls - walked to the footbridge. Vernal and Nevada Falls are also year round waterfalls.
- Yosemite Village - welcome center, museum, replica Indian village, food
- Happy Isle
- Tioga Road
- Tenaya Lake
- Parson's Lodge and Soda Springs
- Olmsted Point - liked this as it was a view of the valley (like Glacier point but from the other direction)
- Tuolumne Meadow - standing there seeing the meadow that Muir was in love with was indescribable
4. Lassen Volcanic. Last on my list because it is out of the way, small. You have to intentionally decide to go there because it isn't on the way to anywhere. 1 day.
- Subway Cave. Lava tube you hike through. It is outside the park in the National Forest.
- Lily Pond Trail - start the trail across from the visitor center. Look for the trail entrance where the leaflet is available so you can read about the stops.
- Devastated Area - interpretive trail through the area the last volcanic eruption devastated.
- Sulphur works - a few mud pots and thermals.
- Bumpass Hell - thermal area similar to Yellowstone
There was a lot of driving. Yosemite to Lassen was 5 hours; Lassen to Redwoods 4 hours; Redwoods to Crater Lake 4 hours.
Good luck in your planning and all our NP visits.