The mystery-laden Grič Tunnel that connects Mesnička and Radićeva streets opened to the public in the summer of 2016. Built in 1943 for use as a WWII air-raid shelter and rarely used since (except for the legendary rave party that took place here in 1993), this 350m-long tunnel is now yours to cross.
There's nothing to see inside but walking under the Upper Town is a great way to beat the heat. Enter from Mesnička or by the Art Park below Stross and get out in a passageway just off Ilica, next door to NAMA department store. There are ambitious plans to turn the tunnel into an interactive Museum of the Senses.