In the east corner of the inner courtyard lies the original well , drilled vertically through of bedrock . The castle keep is surrounded by a ring wall which encloses the bailey . A further forecourt is enclosed by another ring wall . At the south side of this ring wall was the entrance to the estate . On 18 October 1356 , a powerful earthquake shook the Rhine rift ; the donjon collapsed onto the eastern and southeastern buildings . Beginning about 1370 , large-scale reconstruction and expansion of the castle took place . The donjon was demolished , the entrance to the keep relocated and the northern shield wall was closed and raised . The entrance to the castle is now in the southwest corner , where it is protected by the south tower and an inner bailey
a powerful earthquake
1356 Basel earthquake
Auerbach Castle