The seaward face of the old Tudor and Georgian fortifications, now a flat stone-paved promenade running from the Round Tower south to the Square Tower. The name comes from the heated cannonballs (used to set enemy ships alight) once stored in furnaces inside the wall.
A row of artist studios occupies the old casemates under the wall; a small cafe at the southern end has tables outside. Locals come down with chips on a summer evening to watch the cross-Channel ferries set off and the Brittany Ferries flagship glide past at fifteen metres.