If you would want one in the netherlands you could add Breda., bigger than some of the ones I didnt know on here.
Never heard of 6 (bydgoszcz (If I had heard of that one I would ve thought someone was just making a random sound haha) brescia, brest, brno, bari and burgas)
Location can be split. I think worldwide western europe is a bit more know than eastern (besides capitals) And there is the fact how close something is to you. People from poland are more likely to guess polish cities right than serbian.
Eastern Europe: Nah!