S:t Per Gallerian (“The Saint Peter Shopping Centre”) occupies the entire block bounded by Svartbäcksgatan, Klostergatan, S:t Persgatan, and Dragarbrunnsgatan. It has entrances on all of those streets except Klostergatan, and one on the corner of Svartbäcksgatan and S:t Persgatan.
Interestingly, the centre has a “bite” out of the Svartbäcksgatan side to accomodate Celsius huset (“The Celsius House”).
As well as the Clas Ohlson hardware store, there are Cirrus ATMs: just inside the S:t Persgatan entrance is a Cirrus and credit card-capable Bankomat. There is a red Uttag ATM in the ICA City shop, which also appears to take Cirrus ATM cards and credit-cards, but I haven't verified that it works.
Directions
From Stora Torget, walk 100m northwest up Svartbäcksgatan, the pedestrianised street on the even-numbered side of Stora Torget with a Max fast-food restaurant on the corner; the entrance is just at junction with S:t Persgatan.