St Lawrence Church Ruin is one of Sigtuna's medieval fragments, reduced now mostly to a surviving tower. The church was built in the first half of the 12th century, later reused as a school after the Reformation, and destroyed by fire in 1658.
It is a short stop, but it adds another layer to Sigtuna's old-town walk. Pair it with St Mary's Church, the museum, and the town's runestones to see how much early Swedish history is packed into a small area.