Prokopské údolí is the limestone valley the city forgot to build over — a protected karst gash in south-west Prague where 400-million-year-old rock, old quarries and woodland share the same narrow floor. Four and a half kilometres downhill, best in the morning, when the light is in the cliffs and the path is yours.
Start at Nové Butovice and walk down off the plateau; the estates fall away and the údolí (valley) opens. The cliffs are Devonian limestone, laid down under a warm sea and dense with fossils — look, don't hammer, this is a reserve. Past them the old quarry faces are going quietly back to scrub, the post-industrial layer that makes the valley odd. Prokop lake, flooding a former pit, is the turnaround and the place to sit; foxes work these meadows, though you'll likely just hear birds.
The walk lands at the Hlubočepy viaduct, a stone railway bridge striding across the valley mouth — stand under it for the scale, and watch for a train. Then the tram from Hlubočepy back toward Smíchov.
