My name for the place, not the park's.
The grotto upstream from the main falls at Illinois Canyon is seldom
seen by visitors, and the park would like it to stay that way.
The place is accessible only after a few days of very cold weather freezes
the surface of the deep pond below the falls. Even then, a visit is a
dangerous undertaking. A breakthrough while hiking on the pond ice at
zero degrees fahrenheit will ruin anyone's day.