Bidar Fort is the city's main sight and the place where its history makes the most sense. The walls wrap around the old citadel on a plateau of red laterite, with moats, bastions, gateways and scattered palace remains. It is not as manicured as the forts on the standard tourist trail, and that is part of its appeal: you can still feel the scale of a working sultanate capital without being pushed through a fixed route.
Inside, look for the Rangin Mahal, Tarkash Mahal, old audience halls and the massive mosque. Some areas may be closed or poorly signed, so it helps to hire a local guide at the entrance if one is available. Go in the morning before the stone begins to radiate heat.