The grotto, once the most beautiful place in the Forest, led to a silent underground palace with long, deep passages and vaulted chambers, all cut within the limestone hill by millions of years of rain.
It was high noon as Zac and Pook approached the blackened boulders under the hill with the jewels that Zac had found
20 miles south of St. Louis you will find a place called:

Mastadon State Historic Site, a part of the Missouri Parks and Historic Sites

Within this historic site is a trail called Limestone Hill Trail.

here is a map...and darn if it doesn't look familiar...of the trail (see Trail #1)