Famous for its free summer music concerts in the park.

Also see Parks for info on other local parks

Why does it look like a hand?

If you look at aerial photos of Stern Grove, it looks a bit like an upturned hand holding something:

From Google Maps, 2017

This seems to be natural rather than intentional though. The USGS has a nice viewer for old topological maps, and this map from 1896 shows a low-lying area with a pond and stream off to the right, in approximately the current shape of the park:

From USGS, 1896