The name Pui To Shan derives from Pui To Sim Shi, a Buddhist monk whose story has been carried in Cantonese memory for centuries. In the Cantonese reading of his name, Pui means cup, To means water-crossing, and Sim Shi means Monk of Zen. The legend holds that he traveled across the water — miraculously, improbably, in a cup — and arrived at this peak. He climbed the hill and established a monastery on its slopes. That monastery became the Tsing Shan Monastery, which still stands today. Early records suggest the peak itself was once an island, known as Tuen Mun Island, and that its former channel with the neighboring Kau Keng Shan formed part of an important sea route through South China. Defense structures were built on both hills. The monk's improbable arrival by cup feels like exactly the kind of story that accumulates around a place that has always mattered.

Castle Peak is the highest granitic hill in Hong Kong — a distinction that carries geological weight. Granite weathers differently from other rock types. It fractures along joints and exfoliates in sheets, shedding surface layers over time, which is exactly what has happened here. The severe loss of vegetation on the slopes is both cause and consequence of this process: without deep soil and plant cover to anchor the surface, erosion accelerates; erosion removes the material that soil needs to form. The result is a triangular peak — visually striking, almost geometric — with two companion summits to its north and south, at 539 metres and 517 metres respectively. From below, in Tuen Mun, the hill presents as a classic sharp peak. From the air, the bare granite surfaces catch light differently from the surrounding vegetated hills, making Castle Peak immediately identifiable.

Below the summit, the hinterland of Castle Peak carries its own complicated status. Much of this rocky terrain is a designated firing range used by the People's Liberation Army and Hong Kong police forces — the Tsing Shan Firing Range. Warnings are issued before live exercises. The range is sometimes open to the public, but access requires checking Hong Kong Government press releases, typically published one week before each month's schedule. Generally, weekends and public holidays are open days. Within this restricted hinterland, sub-peaks including Kon Shan and Por Lo Shan attract hikers who compare the terrain to a miniature Grand Canyon — broken, layered, dramatic in a way that surprises people expecting soft Hong Kong countryside. The summit itself is not part of the firing range and is accessible daily, though certain routes from the north and west may be closed on exercise days.

Hong Kong's hiking community designates Castle Peak as one of the territory's Three Sharp Peaks — a distinction based not just on elevation but on the character of the ascent. The hike from Yeung Tsing Road in Tuen Mun, beginning just past the Tsing Shan Monastery sign, is essentially a staircase: a series of steps that climbs relentlessly to the 583-metre summit. The straightforward route is exactly that — up the stairs, then back down. But there are options into the hinterland that are steep, slippery, and should not be underestimated. At the top, on a clear day, the view extends across Tuen Mun and Castle Peak Bay to Lantau Island and the airport beyond. The same route the monk — if the legend is taken seriously — might have climbed after his crossing, a journey that ended in the founding of a monastery that has outlasted every dynasty that once claimed to govern this part of the world.