Devil's Backbone Open Space, Plaster Mill Rd, Loveland, 20 miles from Longmont12 miles of trails which connect to Rimrock Open Space and then Horsetooth Mountain Open Space. About 1.5 miles from the parking lot to the keyhole. This is a really nice easy hike that is only 20 miles from Longmont. Located in Loveland, it is surrounded by communities of homes so it does not feel like you are escaping into nature. Still, the rock formation is stunning and feels quintessentially western. The keyhole - an impressive rock arch - is only about 1.5 miles from the parking lot making it a great destination for kids while the adults will appreciate the view of Longs Peek, Meeker, the Twin Sisters and more.
(As I write this post it is cold and snowy, but these photos were taken only a few weeks ago on a warm and sunny day in January. )
For more local hikes see here and here.