The city's main attraction is a grand yet playful collection of buildings standing just inside the city walls; it was once the residence of the Holy Roman Emperor. The complex comprises three separate groups. The oldest, dating from around 1050, is the Burggrafenburg (Castellan's Castle), with a craggy old pentagonal tower and the bailiff's house. It stands in the center of the complex. To the east is the Kaiserstallung (Imperial Stables), built in the 15th century as a granary and now serving as a youth hostel. The real interest of this vast complex of ancient buildings, however, centers on the westernmost part of the fortress, which begins at the Sinwell Turm (Sinwell Tower). The Kaiserburg Museum is here, a subsidiary of the Germanisches Nationalmuseum that displays ancient armors and has exhibits relating to horsemanship in the imperial era and to the history of the fortress. This section of the castle also has a wonderful Romanesque Doppelkappelle
(Double Chapel). The upper part—richer, larger, and more ornate than the lower chapel—was where the emperor and his family worshipped. Also visit the Rittersaal (Knights' Hall) and the Kaisersaal (Throne Room). Their heavy oak beams, painted ceilings, and sparse interiors have changed little since they were built in the 15th century.