Paria Canyon - People have thru hiked it in 2 days, but it is more likely a 4 day trip: ~45 miles (you will need car transportation). You can go out and back, go out Wirepass Canyon, come bake up Paria Canyon.
If you are looking for a few thrills, you might consider canyoneering in Zion. Zion Outdoor Adventures has some neat trips, ask them about the Subway. Best regards - Jon