Ultra-marathoner Toh Poh Joo walked eight days and 566km across the icy tundra of Canada in 2016 as part of a competition, and to raise funds for The Straits Times School Pocket Money Fund.

So a 150km walk for him now would be almost a casual stroll.

But the 44-year-old has a different mission on Nov 1 when he walks with others in the biennial Let's Take A Walk event. Participants will let their feet do the talking for charity over a distance of 20km, 50km, 100km or 150km.

The funds are for Raleigh Singapore, a registered society of volunteers, and Rare Disorders Society Singapore, a non-profit organisation focused solely on patients with rare diseases such as lysosomal storage disorders, which can manifest as skeletal and joint abnormalities.

Raleigh Singapore, the organiser of the event, is hoping to raise $150,000 this year through registration fees and pledges.

The fund-raising event, now in its 11th edition, raised some $114,000 for Caregivers Alliance and Raleigh Singapore in 2017.

Mr Toh will be tackling the new 150km category, a route that will take him and fellow 150km walkers from the National Museum of Singapore to Jurong West, Punggol, East Coast Park and back to the city. He did the 100km walk previously.

He plans to walk the entire 150km without sleep and complete the event in under 38 hours. In previous years, participants in the 100km walks had 33 hours to complete the distance.

"I want to push my limits and try to finish the walk without taking any naps. But Singapore's weather will also be a challenge, as it can be very hot or it may just rain during the journey," said Mr Toh, who has been volunteering at Raleigh Singapore since 2000 and is also co-chair of this year's event.

The director of facilities management at Raffles Quay Asset Management has a routine that will wear out many shoes and joints. On weekends, he goes out for what he calls shorter walks of between 30km and 40km. He previously did 70km walks for about half a year to condition his body for long distances.

He starts at 4am from Upper Bukit Timah, has lunch at Changi Village at noon and then finishes at East Coast Park at 5pm. "Don't be afraid to take part in long-distance walks. The 20km mark is a reasonable distance. While it is far enough to feel the strain, you're doing it for a good cause," he said.

"Without giving it a try, you'll never know your limits."

Registration for the Nov 1 event is now open at letstakeawalk.sg.