Rincon La Vaca and Rio Grande Pyramid is a 20 mile loop trail located near Lake City, CO. The trail is rated as moderate and primarily used for hiking.
My 13 year old son and I hiked this loop/out and back as our inaugural Colorado backpacking trip. We are from Florida, hike the Smokies extensively, and well, Colorado blew our minds. Period. The entire approach up the valley is filled with super rad stuff, and treats like little strawberries on the edge of the trail for munching! Weminuche pass was impressive, as was the first glimpse we caught of Rio Grande Pyramid. I personally felt like Frodo from Lord of the Rings heading into some mystical uncharted realm. It was a surreal and fantastic experience being able to walk amongst such grand beauty.
We never made the window, but we summited the Pyramid on our second morning and hurried back to the car the same day. My only gripe on this trail was the extensive bark beetle damage. In some places entire mountainsides of pole pines are standing, dead and gray. :(