One of the most enjoyable small museums in Reykjavik, the Icelandic Punk Museum is installed in a former public toilet beneath Bankastræti, a couple of steps below the pavement. It traces the Reykjavik punk and post-punk scene of the late 1970s and 1980s — Þeyr, Purrkur Pillnikk, Sykurmolarnir (the Sugarcubes), and the singer who went on to become Björk.
The interior is graffiti-covered, the lighting is dim, and you can plug into headphones to listen to the records the museum is built around. Admission a few hundred krónur. Allow half an hour.