Phoenix's city park system is one of the largest and best in the world, and the Christiansen Trail gives a nice crash course on what it has to offer. This marathon 10.7-mile trail stretches the width of the Phoenix Mountains Preserve, from Tatum Boulevard on the east to Seventh Avenue on the west. You'll traverse much of the city on foot — mostly off the grid, with a few glimpses into posh neighborhoods. It's thrilling, and a little odd, to be in the middle of the sixth-largest city in the country yet totally immersed in the outdoors. Though the trail's long, there is only about 200 feet of elevation gain, so it's also pretty easy. Don't worry about playing Frogger on busy roads, either, as you'll take tunnels under State Route 51, Cave Creek Road, and Seventh Street. We recommend starting early at the tiny eastern trailhead at Tatum and Tomahawk so you begin the day looking up at Camelback before making your way west, slipping around Piestewa Peak and over toward North Mountain. The scenery gets less impressive as you head west. Arrange a ride from the other side after you've ended in a developed city park with restrooms and full cell coverage.