The Detroit Free Press/Talmer Bank Marathon is a 42.195-km race run every October in Detroit, Michigan, USA and Windsor, Ontario, Canada since 1978. The predecessor to this race was the Motor City Marathon which started in 1963 and featured multiple laps on Belle Isle. The marathon course is international and has featured the Detroit-Windsor Tunnel for all but two years of its existence. From 1978 to 1998 the race started in Windsor and finished in Detroit. The current course crosses the Ambassador Bridge and the Detroit-Windsor Tunnel between Detroit and Windsor. Due to its use of the tunnel, the race is able to boast that it has the only official underwater international mile in the world, as the tunnel runs underneath the Detroit River. The race is a USATF-certified, Boston-qualifier course. (source: wikipedia)