The remains of the feudal castle stand on imposing foundations: 16C rounded bastions, and 17C projecting defences in the style of Vauban. From the terrace of the keep (147 steps), there is a fine view over the town and surrounding wooded slopes, where numerous mineral water springs rise from the schist Taunus Massif. Königstein is well-known as a spa, and has some interesting old buildings such as the 13C town hall.