So if you looked at the photos of Tallinn that i posted earlier you might have noticed the high stone walls. These walls were built way back in the middle ages. In fact this week is a festival celebrating the 800th anniversary of Tallinn. When they built the walls they built them with passages in them. Over time they have been used as a garrison, escape routes, nuclear shelters, bomb shelters during WW2 and even as gathering places. I shall take you from the top to the bottom.
This model shows how big the fortifications were.