The Istanbul Tünel (designated as the F2 line) is an underground funicular that connects Karaköy (lower station) with Beyoğlu (upper station). At approximately 573 meters in length, it began operation on January 17, 1875, making it the second oldest urban rail line in the world and the oldest continuously operating underground transit line in continental Europe.
The concept was devised by French engineer Eugène‑Henri Gavand. He secured approval from Sultan Abdülaziz in 1869, then construction proceeded between 1871 and 1874. Originally, the funicular operated with steam-powered wooden carriages on dual tracks that featured a middle section allowing cars to pass each other.
After modernization in 1971, the line was electrified. Steel-bodied, rubber-tyred vehicles replaced the wooden ones, and the line was reconfigured to a single track with a central passing section. A one-way trip takes about 90 seconds, and each car can carry approximately 170 passengers.
Today, this historic line remains a vital piece of Istanbul's integrated transit network.