Which city's metro system operates on two continents?

Istanbul Metro is the metro system associated with a city that spans two continents, Europe and Asia. Istanbul’s European and Asian districts are separated by the Bosphorus, a strait linking the Black Sea with the Sea of Marmara.

The metro network has lines on both sides of the city. European-side routes include the M1, M2, M3, M7, M9 and M11, while Asian-side routes include the M4, M5 and M8. The two metro networks are not themselves directly joined by a metro line beneath the Bosphorus, so this fact is about the system serving both continental parts of Istanbul rather than one uninterrupted metro ride across the continents.

A common mix-up involves Marmaray. Opened in 2013, Marmaray is a cross-Bosphorus commuter railway, not technically part of the Istanbul Metro. Its undersea tunnel provides the direct rail link between Europe and Asia. Istanbul’s unusual geography nevertheless makes its urban rail network the standard answer to this trivia question.