Answer: New York

When it comes to extremely long tunnel building, the name of the game is water delivery. While there are impressively long tunnels around the world that help cars and trains pass through mountainous terrain, the longest tunnels are all part of water supply systems.

The longest of these tunnels is the Delaware Aqueduct tunnel. It begins in the Catskill Mountains at the Rondout Reservoir (a 2,052 acre lake that holds nearly 50 billion gallons of water) and stretches down to New York City over an impressive 85.1 miles.

The project was completed in 1945 and supplies roughly half of the 1.3 billion gallons of water New York City consumes every day.