Holsten Gate in Lübeck

You're standing at the Holsten Gate, the Holstentor, Lübeck's famous city gate and one of only two city gates still standing. Look at the two round towers with their conical roofs, and the arched entrance in between. It's all red brick, in the Gothic style. Now, which side are you on? It matters. From the city side, the gate looks like one solid building, with lots of windows. From the outside, the field side, you can clearly see three separate parts, with few windows and plenty of gun openings. On that side the walls are 3.5 metres thick, while on the city side they're less than a metre.