The fine brick-built Domkyrka was begun in the 12th century, although most of what you see today is late-14th-century work. It contains carved floor slabs, six altarpieces and the marble sarcophagus of King Erik XIV, Gustav Vasa's son and successor, who died in 1577 after eating pea soup laced with arsenic. Ask about going into the tower; times vary, but it's generally open at 2pm Monday and Thursday and 10.30am Saturday (30kr).
Behind the cathedral is the quaint old-town area Kyrkbacken. Once the student district and now a well-preserved portion of pre-18th-century Västerås, it’s studded with artisans’ workshops.