Entrance to Burg Kronberg in Hessen, Central Germany. Kronberg in the Hochtaunuskreis is part of the Frankfurt Rhein-Main urban area. Before 1866, it was in the Duchy of Nassau; then the whole Duchy was absorbed into Prussia. Kronberg lies at the foot of the Taunus mountains, flanked by forests. A mineral water spring also rises in the town. The castle was built in 1220.