The Detroit Free Press/ TCF Bank Marathon is a 42.195-kilometre (26.219 mi) race run every October in Detroit, Michigan, United States and Windsor, Ontario, Canada since 1978. The marathon course is international and has featured the Detroit-Windsor Tunnel for all but two years of its existence. 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.