The remains of the feudal castle lie on an imposing base: 16C rounded bastions, and 17C projecting defences in the style of Vauban. From the terrace of the keep (166 steps), there is a good view over the town and surrounding wooded slopes, where there are numerous mineral water springs rising from the schist Taunus Massif. Königstein is well-known as a spa, and has interesting old buildings such as the former town hall (13C).