Engineering and architecture are complementary disciplines in this project, that renews the transportation system of the city and converts it into an optimistic symbol of rebirth. The connection between Bilbao and its metropolitan area is expressed chiefly above the earth’s surface, although there are some subterranean stretches such as the one linking Elorrieta to the old quarter on the Plentzia-Basauri line, where curved galleries reveal the inherent form of the perforation system. Suspended from the tunnel vault, the lobbies and staircases are conceived as free and light elements. The mouths of the stations are designed as glass chrysalids, easily recognizable by their users and assimilable into any urban context. The minimalist immaculacy of the design extends to the details, among which is counted a meticulous sign system.