Running across sand dunes up to 150m tall and in temperatures close to 50 deg Celsius is bad enough.
But enduring all that while suffering from such terrible sunburn that form blisters, or a painful Achilles tendon for a 251km race sounds even worse.
Yet Mr Ian Lye and Mr Chin Wei Chong accomplished the feat. The two Singaporeans ran the distance in six days across the Sahara Desert in a bid to raise $100,000.
The avid runners and dog lovers decided last September that they wanted to take part in the Marathon des Sables (MdS) to raise funds for Save Our Street Dogs (SOSD), a local non-profit animal rescue group.
The MdS, which began on April 6 and ended six days later, is considered the toughest foot race in the world. The route is around five times the distance from Tuas to Changi.
"It was quite tough to run with bad burns on my legs, resulting in huge pustules (blisters) forming on the side," said Mr Lye, 32, who is the head of Terrorism and Insurgency Research at Thomson Reuters.
Mr Chin, 34, the regional director of marketing communications at First Advantage, suffered from an injury midway through the run.
"During the 81km day, which was the longest day, there were so many sand dunes and I was really struggling," said Mr Chin.
"Then I felt a sharp pain to my tendon."
He endured the pain throughout the second half of the marathon, refusing to take painkillers, as he was worried about the side effects.
"The pain was really morale zapping, and running with it was the toughest thing I ever did," said Mr Chin.