Defensive walls from the 13th-14th century built of glacial erratic, with brick in the upper part; current length 1.5 km, average height 5-7 m. Today there are still 14 shell-shaped and 12 rectangular lookouts (including the Gunpowder Tower from the 19th century). Most of the walls and fortifications are devastated. A promenade runs along the walls. Available to visit.