Under Oktogon Square, the tunnels had to be built between the main water pipes and the tram tracks from the Grand Boulevard. They had to elevate a small section of the road, which is visible even today. The 2.85-metre tall tunnel runs between the surface and the water pipes. From Gizella Square to City Park – where the tracks came up to the surface (behind today’s Heroes Square) – 141,185 cubic metres of dirt was dug up. For the base and the coating of the tunnel more than 52,000 cubic metres of concrete was used, made from Portland cement from Lábatlan and gravel from the Danube.