My favorite is Mt St Helens. 5 miles but that is the deceptive part of it. The hike is straight up: 4,500 elevation gain over 5 miles. It is classified as a Strenuous Hike / Easy Climb. It's one like no other I've ever been on. It is basically chunked into thirds. 1st phase is the nice pretty hike through the trees. 2nd is the boulder climb- no trail just climbing boulders that blew off the top during the eruption. Climb to one post marker, look for the next and start making your way there. The 3rd is by far the most difficult, the straight up "ash fall" of loose and powdery ash/rock/sand. 1 step up only to slide back 2. It's certainly work to get there, but man it was pretty. Best and most ironic part of it was, I finally make it to the top after 4 hours and there's only like 8 people up there. 5 of them were from Iowa wearing Iowa State shirts. It was their 2nd time, the parents brought their kids back now that they were bigger, older, and stronger.