The top of the Grade A++ (very large, perfectly formed arch) Sky Bridge can be reached by walking on a paved trail (Class 1.0) a short distance. But if you want to see the underside of the arch, cross the arch and follow the well-worn (sometimes paved) trail. The entire 0.75-mile loop is a Class 1.0 hike even though there are maybe 60 stair steps at the end to get you back to the parking lot. I found that going down the stairs first (a counter-clockwise loop) is easier, somehow.
With the pillar on one side, is Sky Bridge a double arch? One of the unique things about Sky Bridge is that you can see it from the road next to the Red River.