St Peter's Church Ruin is one of the medieval stone-church remains that give Sigtuna its depth beyond the pretty main street. The ruin is usually dated to the 12th century, when the town was an important religious and trading centre in early Sweden.
It takes only a few minutes to see, but it belongs to a rewarding walk through Sigtuna's runestones, church ruins, lakefront, and old wooden houses. Treat it as one piece of the town's unusually visible early history.