This Gothic tower used to be a part of the city fortifications and now serves as a seat of the Polish Marine Club.
Wikipedia (Polish) http://pl.wikipedia.org/wiki/Baszta_%C5%81ab%C4%99d%C5%BA
Address 5 Targ Rybny, Gdańsk 80-838, Poland
Coordinates 54°21'12.249" N 18°39'29.037" E