Three men in their 50s, who have been going on walks together monthly for about 10 years, wanted to challenge themselves by walking a distance 10 times the maximum they had covered before.
That was the reason they signed up for a free 100km round-the-island overnight trek, which began last Saturday at Raffles Place.
"We wanted to gain a sense of accomplishment... we also believed in teamwork and encouraged one another," said technical officer Ong Chin Bok, 56.
His friend, Mr Alex Quah, a 54-year-old counsellor, added: "We speak the same language."
Together with retired odd-job worker Steven Chee, 59, they were among seven people who completed the journey in about a day as of 10pm yesterday.
The group crossed landmarks such as Changi Village, Chinese Garden in Jurong East and HortPark in Alexandra Road, before finishing where they started, in the city.
The seven were the only ones to complete the journey out of the more than 150 people who participated, with 27 making it to the 50km mark at Waterway Point in Punggol in the north-east. But not everyone had intended to complete the entire distance.
The event was organised by walking enthusiast and project manager Vijay Kumar, 36, who runs the SGTrek Expeditions and Adventures Facebook page.
The most challenging stretch for the three men was along Tanah Merah Coast Road, which was more than 10km long and took them about four hours to complete.
"From the start, we already knew we wanted to complete 100km. We just didn't know how long we would take or how we would do it," said Mr Ong.
The finishers were rewarded with a T-shirt and a lifetime membership with SGTrek Expeditions and Adventures, which was started 41/2 years ago.
Mr Vijay is planning a 50km walk in August - a more manageable distance so that more people can participate.
Yesterday, the first to finish was Indian national Vijayalakshmi Rajulupati, who is in her 40s. The assistant vice-president in a bank trained by walking 5km to 10km every day for two weeks before the challenge.
"My husband and I have been living in Singapore for seven years and we got married here. I love each and every bit of the life here, so it wasn't a boring walk for me."
She added: "If there's a chance to walk 200km for Singapore's bicentennial celebrations this year, I would be interested to do it."