Valkenburg's main draw is its ruined castle perched on the sandstone hill above the town, with the cave system carved through the rock beneath it. The caves — used variously as marl quarries, ammunition storage, bomb shelters, and even a chapel — give the town its distinctive underground character. Several cave systems are open for tours, each with a different angle on local history.
The Cauberg climb brings cycling pilgrims to Valkenburg: this is where the UCI Road World Championships have been decided multiple times and where Tour de France stages have finished. Outside cycling season, the Geul valley makes excellent walking country — the hills are modest by any serious standard, but the landscape of meadows, orchards, and small villages is genuinely lovely.