Three months ago, two cousins became the first Singaporeans to run seven marathons in seven continents over seven consecutive days.
Now they plan to run yet another marathon, in the North Pole.
Mr Ong Tze Boon, 47, and Mr Ong Yu-Phing, 46 - the son and nephew of the late former President Ong Teng Cheong - will join Ms Gloria Lau, 64, as Singaporeans running in the North Pole Marathon on Saturday.
In January, the Ong cousins took part in the World Marathon Challenge (WMC), running 295km in seven continents in seven days.
Through the WMC and the North Pole race, they hope to raise funds for five charities that support mental health: Alzheimer's Disease Association, Caregivers Alliance Limited, Samaritans of Singapore, Singapore Association for Mental Health and We Care Community Services.
"Mental health is very under-appreciated as a social cause," said Mr Ong Yu-Phing, an IT director at an environmental design solutions firm Ong & Ong.
The cousins have already raised around $200,000, including $25,000 from the firm's philanthropic arm, Ong Foundation. All funds raised will go to charity.
Having run in the Sahara desert, which has similar terrain to that in the North Pole, Mr Ong said he was more concerned about the cold.
He said: "If you don't run, you'll get very cold. If you run and sweat too much, you also get very cold."
It could be a challenge to strike that balance, he said. The temperature is expected to be about minus 45 deg C.
For Mr Ong Tze Boon, group executive chairman at Ong & Ong, he will take four goggles to the North Pole. When he ran in Antarctica, his only pair of goggles fogged up, so he ran 10km without goggles.
"I started getting snow blindness. I couldn't see the terrain. Everything was white to me. The only orientation I had was Yu-Phing because he was wearing black."
But he is excited to take part in the North Pole race. Completing it would allow them to join 73 members of the Marathon Grand Slam Club - for those who complete a marathon on each of the seven continents and the Arctic Ocean - and boost their fund-raising drive.
• To donate, go to runwithyourheart.ongfoundation.org
Correction note: An earlier version of this story stated that completing the North Pole race would allow the cousins to join 37 members of the Marathon Grand Slam Club. There are actually 73 members. We are sorry for the error.