You might want to spend some time browsing the exhibits at Bunker Museum, Museum of the World Ocean, or B-413 Submarine Museum. Ruins of Koenigsberg castle, Amber Museum, and Brandenburg Gate are well-known local landmarks worth a visit. You can watch performances at Kaliningrad Regional Musical Theatre, Kaliningrad Regional Drama Theatre, and Kaliningrad Regional Youth Theater for Young Spectators if you're interested in local theater.