Bunker Storm Drain, Warrington

Hidden beneath the southern part of Warrington is Bunker, a vast concrete storm drainage system constructed during the late 1980s to help protect the expanding town from flooding. Built to cope with an extreme 1-in-30-year storm event, the system carries excess water from the surrounding catchment underground before eventually discharging into the Manchester Ship Canal.

The system stretches for roughly 5km, consisting largely of large reinforced concrete pipes, some several feet in diameter. Along its route are numerous chambers, junctions, stairways and dramatic changes in level. One of its most distinctive features is the large swirl chamber, designed to dissipate the energy of incoming water before it enters the main drain.

The name Bunker is believed to have stuck because of the distinctive concrete outfall at the Manchester Ship Canal, which has a bunker-like appearance. Despite being a relatively modern piece of infrastructure, the scale and unusual architecture of the system have made it a long-standing favourite among urban explorers.