Szemlő-hegyi Cave

This guide to Szemlő-hegyi Cave in Budapest starts with a 1930 quarry blast that tore open a hillside and uncovered an unusual cave, among those watching a young man named Hubert Keszler who would spend decades studying it. It explains how the cave formed backward from most others, built up by mineral-rich thermal water rather than carved by it, leaving walls covered in grape-like clusters and gypsum crystals. Look closely at the stone as you pass; locals call it Budapest's underground flower garden.