I actually thought that was most of the Park, so I wanted to hike some areas outside of the main section of Arches. (In retrospect, the areas inside the "main area" and beyond the boundaries of Arches and Canyonlands are numerous enough that I want to get back there relatively soon. Unfortunately, I didn't have as much time to research additional areas before my May trip).
The trailhead is located on UT-128, three miles east of US-191. The trail ends at a large natural bridge, "Morning Glory Bridge."
The trail begins adjacent to a small creek, which is your company for much of this hike. In places, the creek undercut sandstone. In other areas, the valley is wide.
The water, of course, also undercut the natural bridge (by definition). It's still set up right against a cliff, however, and so not super obvious or easily seen until you're practically there.
It's a little over four miles, out and back and about 400 feet of altitude change. So that's mostly flat, although obviously uphill, some, since the water's running towards you the entire way. Several stream crossings, too but an easy hike, at least when I went.