02 February, 1978:
While in a different form than what I have now, when the party was adventuring outdoors I used a version of my 1E Random Wilderness Tables (found in the archives below). I had a large list of outdoor/subterranean areas mapped to use as plot points when the party discovered them, which saved me time creating a layout.
On said tables, I have a section covering Caves, which gives a few options for quick creation of an animal den, altar, or fey circle. One of those was my take after visiting Falling Water http://www.fallingwater.org/ the previous fall in nearby Pennslvania. I loved the idea of a sunlit grotto surrounded by waterfalls, leading to all sorts of possibilities. I wanted an area that in springtime could flood, but featured three waterfalls, paths that were silt covered and yet left plenty to explore. Hence, "Grotto of Running Waters" was born - 1st a full version with stone hatching, followed by a easy print option: