Unveiling London Bridge’s Secret Hollow Interior
The article details a rare expedition through the hollow interior of the Modern London Bridge (1973-present), revealing its surprising engineering and hidden features. Unlike its predecessors, the Old London Bridge (with houses) and John Rennie’s Bridge (sold to Arizona), the current structure is a prestressed-concrete box girder design, meaning it's largely hollow. This bridge, like all non-rail City crossings, is managed by the venerable City Bridge Foundation, a 700-year-old charity that funded its construction without public money and provides £30 million in grants annually.
The journey begins with a challenging squeeze through a small aperture, requiring high-vis gear and emergency breathing apparatus. Despite this initial tight spot, the interior quickly opens into a sequence of surprisingly spacious chambers. The explorer navigates eight long tunnels, discovering remnants of John Rennie’s 1831 bridge, such as brickwork grafted onto the modern structure's north-east corner. Inside, one chamber revealed the defunct underfloor heating system, designed to melt ice at 1℃ and snow at 0.5℃. Further along, a side opening led to a unique “balcony” offering unparalleled views of boats passing beneath, one of London's least visited vantage points.
The interior showcases the bridge's remarkable engineering; its entire weight and traffic are supported by just eight dinner-plate sized supports per pier. The concrete structure also provides exceptional sound insulation, rendering the constant traffic overhead barely audible, and its watertight design prevents common urban smells. The expedition concludes near the south bank, where the largest remnant of Rennie’s bridge – an arch on Tooley Street – is visible, with further sections hidden in a secret chamber used by a gun club. The experience fostered a deep appreciation for the bridge’s “functional grace” and sound engineering, despite its unassuming exterior.
(Source: https://londonist.com/london/history/london-bridge-is-hollow-and-we-walked-through-it)
