You could be forgiven for thinking, if even briefly, that you were on the luscious Waterfall Trail in Prospect Park when you visit the newly-opened Brooklyn Bavarian Biergarten at Grand Prospect Hall in Park Slope. Situated a stone’s throw from a major underpass of the Prospect Expressway, the biergarten is a veritable oasis filled with leafy mature trees, fountains, a stream and yes, charming waterfalls.