Laura Murphy knew her long-standing boyfriend was planning to propose to her, but decided to beat him to it.
To make the occasion extra special she chose to do it 300ft underground in a heritage coal mine.
During the tour of the Big Pit, in south east Wales, the lights were switched off so everybody could experience the darkness.
When the lights were turned back on, Laura, 25, of Leicester, was on one knee ready to ask the question.
The De Montfort University student described it as the most nerve-wracking moment of her life.
"I had planned to read out a short poem but I was so nervous, I ended up just mumbling, 'will you marry me?'
"No wonder girls wait for the men to do it."
Boyfriend Callum Tharratt, 24, also of Leicester, had no idea what his girlfriend of one-and-a-half years was planning.
Callum, who works in construction, said: "I'm still excited, I just can't get my head around it."
Laura said: "He was so shocked, he couldn't speak through his tears.
"I know he was planning to propose to me but I wanted to get in there first."
The mother-of-one said she liked to be quirky and different, rather than traditional.
Callum had always wanted to visit the Big Pit and Laura decided to make their first visit extra special.
Callum said: "I didn't have a clue, I was blown away. It was amazing and I couldn't have asked for anything more.
"Me being Mr Emotional, I just couldn't help getting teary.
"This has made us a proper family, it's made my life and I'm over the moon."
He said he was surprised his fiancee managed to keep the secret from him.
"She didn't let me know anything, I don't know how she did it," he said.
"I think girls should do it more often. They don't understand how it makes a man feel.
"I hate all of this traditional stuff. Our wedding is going to be authentic and different."
The couple, who are hoping to marry in the summer of 2015, said everybody thought it was fantastic.
He said: "All my mates think it's the best proposal they've heard of, they love it."
Laura, who studies nursing, chose to give him a titanium ring, with a small diamond in it.
Callum said: "She did really well. I absolutely love the ring, it is so nice and so me. And it has a little bit of bling, which is what I need."
"This is all I've ever wanted and, hopefully, we'll have a long life together."
Laura said: "He's my best friend and everything else rolled into one and I can't wait to spend the rest of my life with him."
