Abstract: A tower portion for a wind turbine includes at least one wall segment and at least one opening segment. The opening segment includes an opening, one or more inner edges, two side edges, an upper edge and a lower edge, the opening being delimited by the one or more inner edges. The wall segment is shaped as less than a full 360° ring. The opening segment is coupled with the wall segment by the side edges. The opening segment and the wall segment form segments of a ring and when coupled form a full 360° ring. The opening segment has a variable thickness increasing from the side edges to the inner edges.