Nitra Castle dominates the city from its hilltop in the Old Town, a layered complex of fortifications, a bishop's palace, and three churches accumulated over a millennium. The oldest foundations go back to the 9th century Great Moravian period, though most of what you see today reflects Gothic, Renaissance, and Baroque rebuilding from the 13th to 18th centuries. It is not a ruin — the cathedral and episcopal residence inside the walls are still active — which gives the whole complex a lived-in quality unusual for Central European castle sites.
The upper castle contains St. Emmeram's Cathedral, actually three churches in one: the Upper Church (largely Baroque), the Lower Church with its Romanesque crypt, and the Chapel of St. Emmeram, all connected and all open to visitors. The views from the ramparts over the Nitra valley are the best in the region. The castle complex is free to enter; the cathedral charges a small fee.