Right next to Kiek in de Kök defence tower lays the entrance to the Bastion passages, which form a tunnel system underneath Tallinn. These tunnels have been in use since the 17th century and have served many purposes such as storing weaponry, spying on enemies, and even as bomb shelters. Today, the bastion tunnels can be visited as part of a guided tour which will take you on a journey in time – from medieval times up to the year 2219.