But it is not only the city’s tourist board that should be thanking Lee, and producer brother Ben, for a film that does not shy away from the gruesome ordeal competitors experience as they traverse Hong Kong’s four major trails, MacLehose, Wilson, Hong Kong and Lantau.

This is a brilliant study of the human ability to withstand extreme mental and physical hardship.

The viewer becomes familiar with half of the 18 competitors, and it is a tribute to the skill of the storytelling that you quickly care deeply what happens to each of them.

Andre Blumberg, who dreamt up this unforgiving examination of human spirit, and launched HK4TUC in 2011, called the film “a love letter to Hong Kong and human resilience”.

What it is not, is a love letter to running. Know how as a kid you watched Wimbledon on television, then raced to the nearest tennis court? Well, you are made of unique stuff if you see participants sleeping on benches, unable to stomach food, vomiting, and hallucinating - Nikki Han, HK4TUC’s first female finisher recalls seeing “witches on broomsticks” - and feel an urge to slip on your trail shoes.

There are laugh-out-loud moments, notably Hyun Chang Chung’s description of Blumberg when he addresses the tightening of metaphorical strait-jackets on competitors.

The runners must be self-sufficient, throughout, and we see Chung seriously considering a snooze on the floor of a 7-Eleven, after buying instant noodles, while trekking poles and music have been banned.

HK4TUC: Ihara’s incredible act of sportsmanship on way to second finish

Chung’s dry humour, and charming weakness for a beer, position him among the film’s stars. And you would need a heart of stone to not warm to Law Kai-pong, whose gruesome pre-race injury is shown in graphic detail. Law wanted to finish in fewer than 53 hours, but by the time he is falling asleep on staircase bannisters, then conking out in the back of a stranger’s car, that ambition has been superseded by the simple desire to ‘finish’. “I have never really felt this awful before,” he whispers.

To qualify as a ‘finisher’ you must complete the 298 kilometres in less than 60 hours. Reaching the final destination, an oddly characterful green postbox in Mui Wo, on Lantau Island, where Blumberg waits to coat you with the contents of a bottle of champagne, qualifies you as a ‘survivor’.

For the 2021, 10-year anniversary edition, only former finishers and survivors were invited.

The holy grail, never achieved before this event, is a sub-50 hour race, and the film’s direction and production are nimble when Jacky Leung’s unexpectedly brisk progress begins to threaten the barrier.

It was anticipated Salomon Wettstein would flirt with the 50-hour mark, and when those dreams blow up we see his wife imploring him to continue. “If he stops now, tomorrow he will hate me for letting him,” she says, as her husband takes his first, reluctant steps on the 50km Hong Kong trail

We see the humility of ‘celebrity’ trail runner Stone Tsang at the apex of his own struggles. Right at the beginning, footage from the climax of the 2017 event shows an exhausted Tsang’s ‘Steve Redgrave moment’, as he pledges to never again tackle HK4TUC.

There are reminders, too, of a complicated time for the world, in the face masks competitors wear on MTRs, and Sarah Pemberton, a survivor from 2020, talking 15 weeks before the race and looking forward to “three days of certainty”.

Will Hayward, a professor of psychology, and described by Blumberg as “unbeatable when it comes to being one stubborn b*****d”, sources deep fascination from the tricks his mind performs on him at the height of exhaustion.

His nugget of advice for would-be ultra runners is to nap somewhere uncomfortable, such as the top of a rock. “You are that tired, you will fall asleep, but uncomfortable, so you will wake up after five minutes.”

Cramming all these stories and vignettes into 101 minutes, from roughly 150 hours of footage, is an editorial triumph. The film speeds along at a much faster pace than any of the competitors, and the commentary from multiple contributors is sharp and insightful, without ever getting bogged down in detail.

It was an unmitigated hit at last year’s Hong Kong Asian Film Festival, and next month will be shown at the prestigious Boulder International Film Festival in Colorado. Netflix are on a list of high-end potential buyers. It would be money well spent, and transport a fabulous Hong Kong story around the world.