mac_aaron님의 댓글

Reporting 15 S grades is enough to unlock all 4 bonus levels. My ranks: 15S, 2A, 2F, 1E - all bonus unlocked.

That is the Książ Castle http://en.wikipedia.org/wiki/Ksi%C4%85%C5%BC I live nearby (15min on the bike) :D

Seens easy untill last lvl... Hard badge is really hard thanks to boss...