SINGAPORE - They were not aware that the cliff face they were about to climb had been deemed dangerous because of loose rocks.
After one of them had scaled up about 20m, his foot dislodged a huge rock and sent it plummeting towards his female friend who was below holding the rope.
Miss Alvina Lee, 23, could see the rock, which is estimated to weigh up to 200kg, plunging towards her. Yet, she opted not to evade it.
It grazed her helmet, fracturing her skull and causing the brain to bleed. It also fractured her right arm. The blow knocked her out and landed her in the intensive care unit of a hospital for five days. She also has nerve damage to her face and ears, which still affects her hearing in the right ear.
All because she would not release the safety rope attached to her friend as he climbed the rock wall.
Now out of hospital, Miss Lee told The New Paper on Monday: "I had two choices - release the rope and watch my friend fall, or hold on and let the rock hit me.
"I chose the latter."
Even as she faded out of consciousness, she had only one thought - don't let go of the rope.
By doing so, she believes she might have saved her friend's life, though she paid a huge price for her bravery.
Ironically, she and her friend would have avoided any risk to their lives had they checked the Dairy Farm Natural Rock Climbing group on Facebook before they attempted to climb the "Super Crack", a popular rock-climbing spot tucked away in the Dairy Farm Quarry at Bukit Timah on Aug 31.
Rock climbers on the Facebook group had warned that a large rock was loose on the cliff face and could seriously injure anyone who was at the bottom.
Miss Lee, a web developer, said: "I didn't do my research."
She was belaying for her friend as he scaled the 10-storey-high stone wall. This meant she had to hold on to the safety rope attached around her friend's harness.
As he reached the 20m mark - about the height of seven HDB storeys - of the wall, she saw his foot dislodge a large rock.
When The New Paper visited the site on Monday, we noticed that the person belaying could only stand on a narrow patch surrounded by rocks and trees. So Miss Lee would have had little space to try to avoid the rock hitting her.
Her male friend was uninjured and shouted for help. Other climbers nearby responded and one of them held on to his safety rope and he managed to climb down on his own.
Miss Lee is thankful that her friend escaped unscathed.