The Hohenbaden — also called Altes Schloss — is the genuinely old castle on the hill above the town, the seat of the Margraves of Baden until lightning damage and a fire in 1599 made it uninhabitable. Since then it has slowly become a romantic ruin, and is one of the largest castle ruins in Germany.
You can climb the keep for views deep into the Black Forest and out west across the Rhine. There is a courtyard restaurant in the surviving lower buildings that serves a long Sunday lunch. A walking trail from town climbs through the Battert rock formation — popular with climbers — to reach the castle in about an hour and a half.