Circuit de Monaco downhill again to a double right-hander called "Portier," named after region of Monaco, before heading into the famous tunnel, a unique feature of a Formula One circuit. (Until 2009 only one other circuit, Detroit in 1982–88, featured a tunnel, but the F1 series now includes racing at the Yas Marina Circuit in Abu Dhabi, which presents a shorter tunnel at the exit of the pit lane.) As well as the change of light making visibility poor, a car can lose 20–30% of its downforce due to the unique aerodynamic properties of the tunnel. The tunnel also presents a unique problem
Circuit des Nations World War II, on this track, similar to Formula 1 or Formula 2 races, as well as non championship ones. In total 5 major events happened on this track between 1946 and 1950. Key pilots came here to compete: among them Giuseppe Farina, Raymond Sommer, Maurice Trintignant, Juan Manuel Fangio, Prince Bira (who had established residency, in Geneva). The closest race-tracks were Aix les Bains – France (Circuit du Lac) and Lausanne (Circuit du Léman or Blécherette). All were temporary urban race-tracks that disappeared shortly after the Le Mans accident in 1955, or before. FIA Grand Prix, Circuit des Nations,