What figurative expression could I use to describe "an abundant source of"? The context is the following:
the Amazon is a true Free University of Sciences and Philosophy, and authentic ___________ of arts and crafts.
I've found "gold mine", but I believe it wouldn't fit here. Other expressions I considered using were: "cellar" and "granary", but I don't know how they sound for a native. Do they sound very far-fetched?
I don't want the sentence to sound too informal, so I guess I should avoid things like golden goose, cash cow, bonanza, El Dorado.