You might want to spend some time browsing the exhibits at Museum of the World Ocean, Bunker Museum, or B-413 Submarine Museum. Ruins of Koenigsberg castle, Timber Bridge, and Amber Museum are monuments to see when you're exploring the area around Cosmonaut Monument. You can watch performances at Kaliningrad Regional Drama Theatre, Kaliningrad Regional Musical Theatre, and Kaliningrad Regional Philharmonic Hall if you're interested in local theater.