2.0 Miles Easy
This is just a tiny fraction of the PCT at Crater Lake National Park which leads out to Grouse Hill, but is a decent backpacking trail for an overnight at the park. The trail starts about 1.5 miles north of Crater Lake's Rim Drive northern junction and has parking across the street and free dispersed camping. The trail leads over to Grouse Hill, which is about 2 miles out-and-back, but this GPS data is only 1 mile out-and-back.
Camping: To camp off of the trail, you first need to register at the park's headquarters to get your backpacking permit, which is free. Fires are prohibited unless you find a preexisting fire pit since fire risks are usually very high in this area.