The Tünel is a historical underground funicular line in Istanbul, Turkey, located at the northern shore of the Golden Horn. It has two stations, connecting the quarters of Karak?y and Beyo?lu. Its tunnel goes uphill from close to sea level and is about 573 metres (1,880 feet) long. After on-site verification by the World Record Certification Agency (WRCA) officials, it is considered the shortest subway line in the world. Inaugurated on January 17, 1875, the Tünel is the second-oldest extant subterranean urban rail line in the world, after the London Underground (1863). At present, the line is still operating normally, with an interval of 3.5 minutes, and each one-way journey takes 1.5 minutes.