This great observatory is 3km from the city of Jena, Germany. The 6m diameter dome hosts the 50cm F20 Cassegrain Telescope built by students at Carl Zeiss. What makes it unique is that the tracking system is fully mechanical and no power is needed. I have heard that if the system is calibrated right it is possible to reach 5min exposure times which is a challenge even for modern mounts. The observatory and the telescope is run by the local astronomical association Urania Jena e.V.
More information: http://www.urania-sternwarte.de/index.php?id=31