The Ex-Sham Shui Po Service Reservoir was completed on 10 August 1904, near the end of the Victorian era and at a moment when Kowloon was still in early stages of British development. The structure was built in the Romanesque architectural style — arched brick vaults supporting a cement roof, the same idiom that had travelled from ancient Rome to Norman England to the British Empire's engineering vocabulary.

It was designed to serve the residents of Kowloon Tong, Sham Shui Po, and Tai Hang Tung — a gravity-fed distribution point that held water and released it under pressure to the buildings below. For sixty-six years it did exactly that. In 1970, when the larger Shek Kip Mei Fresh Water Service Reservoir came online, the old reservoir on Woh Chai Shan was decommissioned. It sat sealed on the hillside, its vaulted interior intact, for the next fifty years.

What lay inside the sealed structure was not widely known. The Antiquities and Monuments Office had been told about it in a 2017 meeting, when the Water Supplies Department presented plans for demolition. The WSD described the reservoir as a disused "water tank." There was no mention of the brick arches. There was no mention of the cavernous space beneath the cement roof. Heritage officials concluded it was "just a normal tank" and raised no objection.

By December 2020, the demolition work had already damaged part of the roof when residents took a closer look. What they found inside — rows of Romanesque brick arches marching into the dark, a vaulted chamber that had been sealed since before most of Hong Kong's current residents were born — was unlike anything most of them had seen in the city. The photographs circulated instantly.

The woman who blocked the drilling machine was not alone for long. A group of citizens converged on the site, demanded that workers stop, and the public outcry that followed was swift enough to halt the demolition the next day. The authorities suspended the work while an emergency assessment was conducted.

The Antiquities and Monuments Office, now under considerable scrutiny, was asked to explain why no objection had been raised in 2017. Its defence — that the WSD had described only a water tank, without disclosing the historic interior — raised uncomfortable questions about how heritage decisions are made when the people providing information have an interest in the outcome. The reservoir had survived underground for over a century. It nearly did not survive a bureaucratic description.

In June 2021, the Antiquities Advisory Board accorded the Ex-Sham Shui Po Service Reservoir Grade I historic building status — the highest designation in Hong Kong's heritage system, reserved for buildings of outstanding significance. Grade I status effectively halts demolition and triggers preservation obligations.

The decision came with a sobering footnote. Investigation revealed that two other century-old service reservoirs — the Hatton Road Service Reservoir and the Magazine Gap Road Service Reservoir — had been demolished in 2011 and 2010 respectively. In both cases, the Antiquities and Monuments Office had raised no objection. They are gone. The Sham Shui Po reservoir survived because a citizen looked inside at the right moment and then refused to step aside.

The reservoir sits beneath Woh Chai Shan — sometimes called Bishop Hill, a nickname whose origin is less clear than the structure beneath it. After the 2021 designation, the Hong Kong Water Supplies Department developed plans to open the reservoir as a heritage attraction, and the government has since created an official website dedicated to the site.

Descending into the vaulted chamber, visitors find a space that feels genuinely remote from the city above — cool, dim, and ordered by the rhythm of brick arches repeating into the dark. The water that once filled it is gone. What remains is the structure itself: Romanesque engineering from 1904, colonial infrastructure adapted from a Roman tradition, hidden in a Kowloon hillside until the December when someone finally thought to look.