The Strait of Dover (Fr pas de Calais) is the strait at the narrowest part of the English Channel, just 33 kilometers wide between Dover and Calais, and is considered by some to be the busiest shipping lane in the world. The Channel Tunnel passes under it.
It is at the end of the English Channel where it reaches the North Sea. It separates northern France from southeast England; the closest cities on both sides are Calais and Dover respectively.
It is a busy waterway because all traffic between the Atlantic Ocean and the North and Baltic Seas must pass here, or make a treacherous and stormy detour to the north of Scotland.
In the past, the most common way for passengers and freight to cross the Strait was on ferries, but now the Channel Tunnel provides a convenient alternative.