Siegen has been around since at least the early thirteenth century and features two "castles" (more like very large, very fancy, very old houses) named Oberes Schloss and Unteres Schloss, both shown below.
Siegen's history is replete with colorful characters, including Heinrich the Rich, Engelbert II of Berg, and Wilhelm Hyacinth.
Siegen has changed a lot. During World War II, the Allies bombed it several times, because it had a crucial railroad. Those bombings erased 80% of the town at that time. After the war, it had just 28,000 inhabitants. By 1975, it had 116,000. Its population has declined a bit since then.