On a quiet Saturday morning at Telok Ayer Street, a small group of people are gathered around a man in front of Thian Hock Keng Temple, trying to imagine a totally different world.

"Where you're standing now, this used to be where the water was," the man says, brandishing an old black-and-white photo of the area.

"In the 19th century, children would be running around buying street food and bullock carts would go by here."

"Imagine the smell - occasionally, the sea breeze would bring relief."

The speaker is 52-year-old engineering-trained Liew Kwong Chin, who is a volunteer guide leading walking tours of historic buildings on weekend mornings.

Called Monumental Walking Tours, these 11/2 hour tours have been run by the Preservation of Sites and Monuments (PSM) division of the National Heritage Board since 2010 to interest people in the history of important buildings.

The tours, which cost $5 a person, cover national monuments such as the Central Fire Station at Hill Street and the Former Telok Ayer Market, now Lau Pa Sat.

They also feature historic sites which are not national monuments but are important in Singapore's history. These include Fuk Tak Chi museum at Telok Ayer Street and Queen Elizabeth Walk at Esplanade Park.

In July, 13 new tours were added, bringing the total number of themed tours offered to more than 30.

These include the Mixed Blessings tour led by Mr Liew that highlights the different religious monuments on Telok Ayer Street.

Besides weekend tours, special tours may also take place during public holidays or the annual Istana Open House.

New tours are also added when new monuments are gazetted.

For example, a new tour, Expressions Of Faith, covers the Sri Thendayuthapani Temple at Tank Road, which was gazetted at the end of last year.

The tours, which can accommodate 15 to 20 people, are well subscribed, having reached out to more than 24,000 people since 2010.

Explaining the popularity, organisers say that there is more curiosity about old buildings and traditions as Singapore progresses as a nation.

Finance worker Ken Tan, 35, who attended the Mixed Blessings tour with her sister, finds the tours a good way to spend weekends.

"The tours cover varied and interesting topics. You get to learn new things about buildings that you think are commonplace, or cultures you grew up with," she says.

The Monumental Walking Tours are led by a group of volunteers, who design their own routes based on their research through books, old articles and National Archive materials, supplemented by notes given by National Heritage Board during their training.

For the more independent- minded, the heritage board also offers self-guided heritage trails, such as the recently revamped Singapore River Walk

One may download the trail route and information about each marked site from its website.

Historian Frederik Rettig, 44, a German permanent resident here, prefers guided tours to self-guided ones.

"Sometimes, I feel a bit shy to enter religious sites," he says. "On a tour, I can do so because the guide has permission to take us into the building."

What sets the Monumental Walking Tours apart is the human touch of the guides.

Of course, it helps that they make the tours a lively experience, often spicing up their talks with interesting personal tales and anecdotes.

History lover Sam Yun-Shan, 33, decided to sign up to be a Monumental Walking Tour guide earlier this year, seeking a different experience from the "controlled environment" of a museum, where she has led tours before.

"With outdoor tours, there's traffic, it's hot and, sometimes, you're talking about something that doesn't exist anymore, so you have to find ways to be engaging," says the civil servant.

The guides often use archive materials, maps and photos to help illustrate their stories.

Sometimes, it is those who attend a tour that bring it to life.

Mr Liew was leading a tour of Raffles Hotel, a national monument gazetted in 1987, in August with a group that included a 92-year-old British woman.

"She told me that she visited the hotel in 1957, the same year that actress Elizabeth Taylor visited," he says. "There's a treasure trove of history around us."