The "Old Castle" near Singhofen is a former Celtic fortress on a prominent conical hill in the Mühlbach valley.
The "Old Castle" was built by the Celts around 400 BC so that they could retreat there in the event of attacks by enemy tribes. Apart from the striking landscape profile, nothing of the "Old Castle" can be recognised today. The Kegelberg, on which the "Old Castle" stood, is a beautiful place whose path leads into the Mühlbach valley.