He says the route highlighted how public estates such as Lek Yuen, the first in Sha Tin, and amenities along Shing Mun River were built on reclaimed land, and showed how Sha Tin Town Plaza had evolved into what it is today.

"To dovetail with the new town development, Sun Hung Kai Properties built the large mall so that residents could live in a self-contained community. We shared stories of how the developer sent people to Japan to persuade the Yaohan retail group to open in the mall," Chan says.

Because all four hold full-time jobs, their tours are held only once a month. The initial events were offered for free but since May they began to charge HK$50 per head to cover operating costs.

Other Hide & Seek walking tours include visits to heritage sites buried among the skyscrapers and glitzy malls of Tsim Sha Tsui and another to the walled villages in Tai Wai.

While many young people hit the malls or clubs during down time, the quartet preferred to explore the older corners of the city and are now putting their knowledge to use.

Wan, an avid collector, plans to bring along small items from his personal hoard (coins, miniature weighing scales and the like) to show visitors during a future tour to traditional shops on Shanghai Street in Yau Ma Tei.

"Those old shops are disappearing fast. We want to let more people know about them before they are gone. The joss stick shops and tea sellers have been there for decades, with some over 100 years old. Many still use old Chinese [weighing] scales which show lots of traditional wisdom."

They are simple devices, he says. Items are placed in a pan hung from a marked stick, and a counterweight hung at the opposite end is moved along the stick until balance is achieved.

Walk in Hong Kong, co-founded by former political assistant Paul Chan Chi-yuen, offers perhaps some of the more knowledgeable guides.

He started the enterprise with two friends, history researcher Haider Kikabhoy and travel writer Chow Chung-wah, after ending his stint as aide to the secretary for Food and Health.

During his mandatory "cool-off" year after leaving public service, he used the time to think about the future. A keen traveller who fondly recalls joining guided walks in Europe, he mulled over their potential here.

"When I was working for the government, a scandal broke about a local tour guide [yelling at visitors for not doing more shopping]. Hong Kong is my home. I want to show the good side of it to visitors. So I thought about the idea of organising walking tours in the city."

Set up in 2013, Walk in Hong Kong now offers nearly 20 different itineraries. A night visit to Yau Ma Tei takes in its wholesale fruit market, Temple Street and the '50s-era Mido Cafe, whose retro decor makes it a favoured location for local filmmakers.

"There are only five or six streets [on the route], but they epitomise '70s Kowloon lifestyle to a tee. We take participants to do palm reading and eat dessert on Temple Street, too. While everything has changed in Hong Kong, that '70s ambience is still there," Chan says.

Kikabhoy, a history researcher at Chinese University, says their jaunts stand out because guides liven up the walk with lots of stories about local people. "Yau Ma Tei fruit market was infamous during the '70s as a hangout for drug dealers, who hid drugs among the fruit. We found a worker who has been there for 40 years to share what he witnessed back then. Visitors often burst out laughing when listening to these stories."

The walks cost between HK$300 and HK$600, with some food provided on pricier outings.

One of three full-time staffers in Walk in Hong Kong, Chan's new role is a big change from his government job which came with a HK$130,000 monthly salary.

"Many guided walks are organised by non-governmental organisations, but we run it as a business. So we must keep HK$500,000 in reserve at the bank to fulfil a requirement of operating a travel agency, and maintain an office."

Although they mostly rely on friends with special expertise to lead the walks - for instance, a lawyer, an architect and a media professional - each has received training and passed the test required for a licensed guide.

The architect leads sophisticated tours of interesting buildings; and international relations scholar Simon Shen Xuhui previously led a tour of the Happy Valley graveyard, which he described as an indicator of early globalisation, with the dead coming from six races and religions.

Another tour, led by political scientist Ray Yep Kin-man from City University who is an expert on the 1967 riots, retraced the steps taken by leftists in the anti-colonial demonstrations in the key communist stronghold of North Point.

"We shared stories about how the home-made 'pineapple bombs' were put together. Instead of reading from a textbook, a walking tour gives people a fun and colourful way of viewing these important events."

Chan usually leads the night tours of Yau Ma Tei, where he grew up; while Kikabhoy guides the walks around Wan Chai - a regular haunt because his 90-year-old grandmother lives there.

"I have been frequenting Wan Chai my whole life. My grandmother has told me many stories about life in the area … how children used to play hopscotch on the covered walkways, even during rush hours," Kikabhoy says.

And as a researcher, he has been able to unearth interesting details about the district to share with visitors. For example, the curvaceous old Wan Chai Market, completed in 1937, was built in the Bauhaus style that was influenced by the "streamlined moderne" movement.

The old civilian airport in Singapore and the central market in Phnom Penh were also built in the same style in the same year.

In Sheung Shui, growing friction over congestion, litter and other problems caused by parallel traders has prompted Chan Shing-yin to starting conducting tours around his home town to help visitors understand how these changes have affected life in the area.

A third-generation resident of Sheung Shui, Chan is organising the walks for the Society for Indigenous Learning, which aims to nurture people's love of the land by organising farming activities, heritage tours, recycling ventures and the like.

His grandfather moved there in the '40s, working at an electronics shop. His father followed eventually, establishing the family's own electronics retail business in the '80s.

On the walk, he describes how clans such as the Lius came to be concentrated in Sheung Shui, as well his family's migration. A history student at Shue Yan University, Chan also explains how Shek Wu Hui has served as the principal market for Sheung Shui area since the '30s.

People have long converged there without conflict as they came to do business, he says.

"But today our community is torn by clashes between visitors [from China] and residents because Sheung Shui has become a haven for parallel traders. I am saddened by it. We hope that our tour can help visitors understand the development of the district and how it has evolved into what it is today."

As the public becomes increasingly aware of heritage conservation, walking tours are bound to attract more visitors. Paul Chan of Walk in Hong Kong is so optimistic about their prospects that he plans to roll out a major expansion of his business next month, with a new website and more frequent tours.

"Our current tours are not run on fixed dates," he says. "But from August, we will run at least five walks every week."