During our family vacation in Utah, we were able to visit Zion National Park. It was incredible (and incredibly hot). My dad really wanted to do a specific hike -- Angel's landing. It's not a particularly long hike (only about 5 miles round trip)...but it's fairly strenuous. Basically - a trail was cut into solid rock in the 1920's and it leads to an amaaazing view of Zion canyon. The final section is real steep, and since there are drop-offs on either side, there's a chain you can hold onto. HOW HANDY. and TERRIFYING. You can see hikers starting to head up in the 4th photo below. Needless to say, since I'm not in great shape (mental note: change that), it was tough. But once we got to the top, the views were unbelievable. It's so rad to be able to experience and see something unlike anything you've seen before.
If you find yourself in Zion (and you're not afraid of heights), I'd definitely recommend Angel's landing. But, if possible, I'd go during the spring or fall... because geez-- 107* whilst hiking is not my cup o' tea. ;)