Barbican

The Barbican is a circular brick fortress that once guarded the main gate into medieval Kraków, and it's the best-preserved example of its kind in Europe. Built in 1498 when the Ottomans were a genuine threat, it's a masterpiece of defensive architecture — three-metre-thick walls, 130 loopholes for crossbowmen, a 24-metre diameter, and a moat that's now a dry ditch filled with tourists taking photos.

The fortress was connected to the Floriańska Gate by a covered passageway that allowed defenders to retreat behind the city walls if the Barbican was overrun. That passageway is gone, but the gate and the Barbican still face each other across a short stretch of the Planty park, and walking between them gives you a compressed experience of approaching a medieval fortified city — open ground, fortress, gate, city.

Inside, the Barbican hosts temporary exhibitions and occasional concerts in summer, but the building itself is the main attraction. The upper gallery, reached by narrow stairs built into the walls, gives you a defender's-eye view of the approach — you can see exactly how exposed an attacker would be, caught between the Barbican's loopholes and the archers on the city walls. It's small enough to see in 20 minutes and atmospheric enough to remember.