Gornji trg Preduh Tunnel in Ljubljana, Slovenia

Between two unassuming residential buildings, not far from the centre of the city, is a strange portal leading any would-be adventurer on a short but mysterious journey into Ljubljana's past.

The tunnel, which stretches just a few meters to the back of the buildings and ends abruptly at a locked door, is just one of many that would have provided ventilation and a fire break between buildings in the middle ages. Almost all of these tunnels have now been blocked up, except this one. In fact, the attention of passers-by are intentionally drawn to this anomaly with decorative lights strung up on the tunnel's ceiling and a plaque to explain its purpose, in multiple languages.

All of this leads the unsuspecting pedestrian to think that this is anything more than simply a means of providing air throughout the buildings and possibly even a channel for disposing of sewage to the street. Hence the affectionate nickname, schießgaße.