The ring wall "Old Castle" is a gem on the Este near Hollenstedt. It is a still recognizable earthen rampart with trench from the late 9th century. This fortified with palisades, also called castle, probably served for defense purposes. It was probably built by Charlemagne and later taken over by Stader Graf (after a fire).The ring wall with the medieval garden is a nice and quiet place. A bench invites you to linger and there is also a self-built barbecue area. The garden, which was created by students and the association Estetal, includes interesting herbs and plants.