Lowry refers to a windmill in Cape Cod in his novel Ultramarine when Dana tells Popplereuter; " At Cape Cod...... I committed my first murder, in a windmill." This is part of Dana's fantasy of his life story which he is telling Popplereuter in their drunken drift around Tsjang-tsjang (Dairen).
Lowry spent several weeks in Cape Cod in the summer of 1929 during his visit to meet Conrad Aiken. Aiken owned a house in Yarmouth on Cape Cod. The windmill most likely Lowry is recalling is the Judah Baker mill.
This windmill takes its name from its original builder, Judah Baker, who had the mill constructed in 1791. Like many early windmills on Cape Cod, this mill experienced several moves before it came to its current location. Originating in South Dennis, it was moved to Kelley's Pond, in Dennis, and later to the Yarmouth side of Bass River. By 1866, it rested near its current location and was used by Braddock Matthews for milling grain. As large commercial mills appeared in the Midwest, local mills, including this one, fell into disuse. In 1953, the mill was donated to the town of Yarmouth along with the surrounding Windmill Park, which includes a small swimming beach on Bass River. In 1999, the windmill underwent an extensive renovation and now appears in its original condition. Historical Society of Yarmouth
Lowry's fantasy may have something to do with his drunken brawl with Aiken in Boston when Lowry managed to fracture Aiken's skull. (Bowker Pursued By Furies Pg. 84)