The Highline Canal Trail is a national landmark trail originally completed to deliver irrigation water to Denver. The mostly gravel trail runs 66 miles (!) from Waterton Canyon south of Denver, traveling east northeast through many of Denver’s southern suburbs, through Aurora and terminating at Green Valley Ranch, about 10 miles from the airport. The trail connects many of Denver’s parks and has some lovely sections shaded by cottonwood trees. There are markings every 1/2 mile. The most scenic stretch is the 6 miles between Three Pond Park (parking) and Orchard Road that takes in the Blackmer Commons Wetland Wildlife Preserve. Another good connection point is Ruby Hill Park, recently renovated, with great views and featuring a snowboard and terrain park.