Armed with evasive speed and a wicked sidestep, the diminutive winger crossed for 58 international tries during his career -- 18 more than any other Welsh player has managed. He also scored a record 57 times for club side Ospreys.

But during his playing days he could hardly have envisaged the record he's about to attempt to break next.

As part of a wider group of 30 adventure-seekers -- including fellow former internationals Lee Mears, Ollie Phillips, and Tamara Taylor -- Williams will attempt to advance up Mount Everest to take part in the highest ever game of rugby.

No stranger to setting himself a challenge, Williams has completed a number of Ironmen -- the grueling distance challenge involving a 2.4-mile swim, a 112-mile cycle, and running marathon -- as well as cycling the length of California and trekking across Patagonia since his retirement from rugby in 2014.

Nothing compares, however, to the challenge presented by Everest.

"As a rugby player, I was a sprinter, so the last thing I ever thought I'd be doing was (the) long distance anaerobic training" required before taking on the world's tallest mountain, the 41-year-old Williams tells CNN Sport.

"But I enjoy keeping fit, I enjoy challenging myself and I enjoy the fact that it takes me completely out of my comfort zone.

"I'll be on this mountain with a group of other people that are in the same position as me. We're all going to have to help each other up that mountain and down it as well and break this Guinness World Record and I quite like that."

Williams scores against Scotland at the 2009 Six Nations

'The unexpected'

Departing on April 13, the 24-day trek will take the party 6,500 meters up Everest where they hope to play the highest game of full contact rugby and the highest game of mixed touch rugby. At least $265,000 will be raised for children's rugby charity Wooden Spoon

The adventure will begin in Chengdu, China, before trekking for over a week across the high passes of Tibet to reach Everest Base Camp.

By the 14th day, the group will have reached Advanced Base Camp, and just beyond that -- at 6,500m -- they will make their world record attempt which would better the current best effort of 5,752m set in 2015 on Kilimanjaro.

"I'm nervous in the sense that I don't know what to expect. I've done nothing to this extreme before," says Williams.

"When I was playing rugby I knew what was coming. I knew who I was playing against, I had done my prep, I knew how difficult it was going to be ... you get battered around the rugby field so you prepare yourself for that.

"But this one, it's the unexpected ... I could walk up there and my fitness could really help me and I can help people get up that mountain; on the other side of it as well, I don't know that the training I've been doing is enough."

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Altitude sickness

The biggest challenge -- and the biggest unknown -- says Williams, is how he copes with the altitude. Even seasoned marathon runners can struggle with altitude sickness, and the effects of being exposed to the snowy slopes of Everest can be debilitating.

At the mountain's 8,848-meter peak, for example, each breath contains one-third of the oxygen found at sea level . Most people can last 20 minutes at the top of Everest before it becomes unbearable.

Williams' team of hikers, of course, won't be attempting to reach the summit, but they will have to run, pass, tackle, and scrum at heights they've never previously experienced.

"I probably underestimating the whole trek," says the former winger. "I do a lot of triathlons and I've done a couple of Iron Men now and I thought I'd be fit enough. If I can run a marathon surely I'm going to be able to do this?

"But recently I've started doing altitude training and realized straight away that it's a lot more difficult than I expected."

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What he's also become aware of is how the challenge is much more than just a physical test. There's the matter of a fundraising target to hit, too.

"People are working really hard to raise these funds, doing events whilst juggling a family and businesses and jobs at the same time," says Williams. "That's blown me away.

"People have been training hard as well. We've had a lot of pictures of people on top of mountains and going for walks with their family and everything. I think it's just brought everyone together so it's great."