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.
Despite their five months of training for the desert run, nothing would have prepared them for the trials they faced during the race.
"The first day was really tough, and over 20 people fell out," said Mr Lye. "Traditionally, MdS tries to give an easier first day but this year they just threw us into the hot water. Just 3km from the start line, we had to tackle huge dunes."
Added Mr Chin: "Some of the veterans said this was the toughest MdS ever."
Said Mr Lye: "On the fourth day, we were on the move from 9am to 7am the next day. We were mentally and physically exhausted."
But what kept them going, apart from each other's support, were the e-mails they received from home.
At the end of each day, the organisers printed out the e-mails for the runners and each runner could send home one e-mail.
"These e-mails were really important to us. After reading them we'd be motivated and ready to run again," said Mr Chin.
One of those who wrote an e-mail to them was Minister for Foreign Affairs and Minister for Law K. Shanmugam, who also posted regular updates on his Facebook page.
"We got an e-mail from the minister encouraging us and saying that the whole country was behind us," said Mr Lye.
"That was really uplifting."
Mr Lye finished 604th, clocking around 51 hours, while Mr Chin finished 644th out of 917 participants, in about 53 hours.
The pair's efforts have helped to raise over $26,680 so far to build a new shelter for SOSD. The fundraiser ends on Monday.
Dr Siew Tuck Wah, 35, president of SOSD, said: "We are very proud of them for completing it and got quite emotional, especially when we saw Ian's photo with the Singapore flag."
Dr Siew is happy with what they have raised.
He said: "Any amount is a bonus, even if we don't reach our $100,000 goal.
"We will be bringing the two of them out to thank them once they come back to Singapore."