Have you visited a National Natural Landmark? Not sure? Then check out this map and click on your state to see if you have some NNLs (561 of them exist) in your area.

NNLs explained: Different from a National Historic Landmark or a unit of the National Landscape Conservation System, a National Natural Landmark, other than being hard to say 3 times fast, is part of a program started in 1962 to "encourage the preservation of the best remaining examples of the nation's biological and geological features in both public and private ownership." Part of the National Park Service system, an NNL designation creates no new land-use restrictions not previously in effect before the landmark became a designated site.

Six new landmarks were added last year. One of them, Hanging Lake NNL in Colorado's lovely Glenwood Canyon near Glenwood Springs, is a personal favorite, right off I-70 that I visited many times during cross-country drives between my home turf (in Ohio) and college town (in California). I'm dating myself, but I visited Hanging Lake back when 2-lane U.S. 6 was the only paved path winding through the canyon. It was one of the best leg-stretchers of the whole trip.

Who else digs Glenwood Canyon? If you've got a NNL that appeals to you, we'd be interested to hear your story.

Photo: Henderson Sloughs NNL in Kentucky (courtesy of the National Park Service)