Nuremberg and the castle it was centered around have a long and storied history. The town was part of the Holy Roman Empire (HRE), which lasted from the rule of Charlemagne in the 800s CE until the founding of the German Empire in 1871. For political history, a millennium is a really long time. The United States have been around for less than a quarter of that.
The Holy Roman Empire morphed throughout its history to include different states, factions, and kooky leaders. Who inherited the title "Roman Emperor" had little to do with Romans and everything to do with the Roman Catholic Church and the lords of the various Germanic lands, who conquered what had been most of the Western Roman Empire after the year 405 CE.
Voltaire once said that the HRE was neither Holy nor Roman nor an Empire. Whatever it was, it was not a highly centralized state, but one made up of hundreds of semi-allied fiefdoms, states, and cities—at times covering most of Europe except for England and western France. For much of its history, the HRE included Italy and Burgundy, in addition to what we now call Germany.
As an important city during the life of the Holy Roman Empire, Nuremberg hosted legislators and court sessions. And like any respectable town in the High Middle Ages, it had a castle.
Though damaged during World War II, the castle has been restored to its original state. The Double Chapel in the center of the castle remained unscathed during the War. The castle offers tours of the Double Chapel, the Imperial Castle, and the Well.
What's more, the old emperor's mews now features a youth hostel where you can sleep like a king... or at the very least like a king's horse.