Lamar Valley Trail is a 7.1 mile lightly trafficked out and back trail located near Yellowstone National Park, WY that features a river and is rated as difficult. The trail offers a number of activity options and is accessible from May until October.
Pros: good fishing, nice views, lots of buffalo
Cons: too busy, poor campsites
I did this last year in late July. The fishing was amazing and I heard other fishermen upstream on the box butte did even better. Tons of little holes loaded with trout, my favorite catch in life was the cutter I brought in on a purple hopper with my wife and kids watching. Recommend bug nets depending on time of year, once dusk and dawn hours were there it was pretty bad. My 8 and 11 year olds were troopers though. No bad inclines and a little water to cross made for some good highlights. We camped but spent evening inside retreating from heavy bug presence.