You were told that National Park Mystery Spot 5 is a place that lots of very tired people have been very happy to see. You were also given these clues:
A ghost of sorts.
Usually large and fenced.
A jenny may take you there.
Here’s the solution:
Another name for ghost is phantom. “Usually large and fenced” is an apt description for a ranch. The solution is Phantom Ranch, an oasis-like cluster of cabins, dormitories, and ancillary facilities (including a mule stable) located on the north side of the Colorado River at the bottom of the Grand Canyon. The concessioner-operated Phantom Ranch, which is on the National Register of Historic Places (architect Mary Colter, constructed 1922), offers the only lodging below the canyon rim in Grand Canyon National Park. Though spartan by modern standards, Phantom Ranch seems like the Hilton after your long hike or ride down into the canyon's bowels on the Bright Angel or North Kaibab Trail.
“A jenny may take you there” relates to the fact that many visitors arrive at Phantom Ranch via mule train. (A female mule is called a jenny.) The other visitors are hikers or Colorado River runners (mostly rafters).
There is a map of Phantom Ranch at this site.