Hohentwiel
Besides having a number of buildings set at different levels of the castle, Hohentwiel also has three distinct entrances that one must pass to reach the heart of the fortress.  Each entrance also correspondes to a distinct level.  It is no wonder it could withstand numerous sieges.
Left, one of the main turrets that guarded the lower entrance.  Above, one of the many remaining ruins of buildings in the lower level.  Below, the entrance to the middle level, and some of the ruins (lower left) on that level.
Left, the third guarded entrance into the upper level.  Below, some of the ruins at the upper level, with FOUR separate stories to the building in the center.
Left, the interior of one building showing the supporting arches to bear the weight of the masonry structure above.  A number of the main buildings at the top have masonry floors over the first story.  Wooden floors predominated above that.