The Vienna U-Bahn is an unofficial gallery of over 20 artworks, surreptitiously lurking in the tunnels of the underground stations. On the mezzanine of the U2 and U1 at Karlsplatz, you will pass work by Austrian artist Peter Kogler. The installation is a series of interconnecting grey tubes, an intriguing departure from the seamless uniformity of the station’s architecture. Kogler’s work functions as a symbol for connection and the winding underground passages of the city’s U-Bahn system. The work was unveiled in 2012 and has since solidified itself as a timeless work in one of Vienna’s busiest commuter routes.