Silesian Ostrava Castle is the city's oldest building, a Gothic and Renaissance fortress on a low hill where the Lučina river meets the Ostravice. Founded in the 13th century to defend the trade route from Moravia to Silesia, it spent most of its life as a manor house before centuries of mining subsidence beneath it caused it to sink about 16 metres into the ground — a slow collapse that is now stabilised but still visible in the leaning walls.
The castle now hosts open-air concerts, a small museum on the history of Ostrava, and a couple of summer beer gardens in the courtyards. It is a pleasant 20-minute walk from the centre and gives a different angle on the industrial sprawl across the river.