Narrows Trail at Zion National Park
Known as the "grandfather of all slot canyons," the Narrows Trail is the most popular in the park, providing an opportunity at one point, to reach out and touch the 2,000 foot, dramatic, parallel rock walls. 60% of the trail is actually in the water, at one point waist deep, as the trail itself is the Virgin River. Sometimes you are walking along the banks, but walking sticks are necessary as it is very rocky and unstable. Wear very sturdy shoes!
Photo courtesy of markbyzewski