The Świętojańska [St. John's] Gate

The Świętojańska Gate (also known as the Szczecin Gate) was built in the 1450s and, originally, was preceded by a gatehouse with a drawbridge, throat and body gateway. The gate defended the way to the town from Szczecin.
Water-earth fortifications in front of the gate were demolished before 1720 by Prince Moritz von Anhalt Dessau. He created there an assault course for the military.
The superstructure of the gate has served as a penitentiary means since 1721, while since 1820, it has housed a mental hospital.
Later, the gate was completely demolished in 1842 and a lancet tunnel was built in its place. Today, the remains of the gate, and actually the gatehouse, can be seen from the street and from its top, because Słowicza Alley runs there. The tunnel runs along Św. Jana Street and there is no pedestrian crossing beneath it.