to get to horseshoe canyon from moab, you head back north up the 191. hang a left onto I-70, but before you hit the san rafael swell (say, 30 miles or so), turn south down 24. a couple dozen miles down that two-lane asphalt you'll see a dirt road leading east to hans flat ranger station. now you need the topo maps. after about 30 miles on increasingly rough roads, you hit the five-mile access to horseshoe canyon. wonder whether you should have a vehicle on this road at all. persevere. and park in the overview parking lot that gives nothing away.
the hike is marked with cairns over slickrock, and it goes down down down for 750 feet. you're not surprised to see dinosaur tracks on the path. every step down gets a little bit hotter, until you're down on the breezeless canyon floor. by early afternoon it's about 32 degrees down there, with the sun glinting off desert-varnished rock.
you walk the wash for a few miles, looking at various petroglyphs and pictograms along the way.
finally, you get to the great gallery, with some of the finest rock art in the world. it's a pilgrimmage for many anthropologists, a mecca for art historians. you sit, awed, in the blessed shade, and you're right: you will never forget this feeling.
on the way home, even though it's in the opposite direction, stop at goblin state park. why not?