When in Stockholm, try this budget attraction—the subway! This really is art underground, literally. It is called the longest art museum in the world. Over 90 of the 100 stations in Stockholm have been decorated with sculptures, mosaics, paintings, installations, engravings, and reliefs, by more than 150 artists.
I spent over three hours here, getting off at each stop to take photos. My favorite line was the blue line, built in the 1970s and left more "natural." All the blastings that take place to build an underground subway are typically covered up with tiles and walls. But the blue line left the rock exposed, which gives you the feeling of a cave as opposed to a subway.
The best part is, this museum costs only the price of a subway ticket! To learn more, visit http://sl.se/Global/Konst/Engelska%20broshyrer/Art-MetroENG_webb.pdf