Cave discovery anniversary marked

In pictures: Peter Collings-Wells' images

Three explorers who discovered a new entrance to one of the UK's major cave systems have returned there to mark the 40th anniversary of that moment.

Two of them, now aged 62, retraced their steps through Ogof Ffynnon Ddu, in the Swansea Valley, from a second entrance they uncovered in 1967.

The cave had been discovered in 1946 but a "through trip" was impossible.

An online "virtual tour" has also been created so people can travel through, and even get lost in, the cave network.

Ogof Ffynnon Ddu, meaning the Cave of the Black Spring, is the deepest and the third longest cave in the UK, according to Peter Collings-Wells of the South Wales Caving Club.

He explained that the cave, at Penwyllt, near Abercrave, was first discovered in August, 1946, by two cavers intrigued by springs of water that surged from the rock after heavy rainfall.

Terry Moon emerging from the cave in 1967

One of them was Peter Harvey, who lives near Brecon, who is now in his 80s but still goes caving and is president of the South Wales Caving Club.

The pair began digging and discovered large cave passages leading away into the mountain.

Mr Collings-Wells, 38, from Hitchin, Hertfordshire, said: "Finally in 1967 they got a long way up the hill, about 300m higher than the lower entrance that was first discovered.

"They got to a point which was very close to the surface. When you get near, you get to see little snails and tree roots shows close to surface."

Seven people were underground with four above - including Mr Harvey. Most were South Wales Caving Club members and communicated using radios.

Mr Collings-Wells said: "The team underground began to dig away and pull down rocks in the way. It was fairly risky.

Around 50km of passages in the cave system have been explored

"There was great excitement because for a number of years they had been searching for an extension."

After pulling enough rocks away, a gap was made and, aided by the team above, the cavers climbed out.

Their breakthrough meant cavers had a "through route" for the first time.

This has since been completed hundreds of times and is, according to Mr Collings-Wells, "one of the biggest challenges of caving."

Mr Harvey and two members of the underground team from 1967, Clive Westlake and Paul Deakin, joined other club members to mark the 40th anniversary on Saturday.

Mr Westlake and Mr Deakin also intended to complete the "through trip" with other club members.

'Virtual tour'

Although the through route should be left to experienced cavers, anyone can experience it using a virtual tour developed online by Mr Collings-Wells.

He said: "I wanted to show people like my mum who never really knew what it is like to go caving."

Part-time photographer Mr Collings-Wells has around 350 photographs on his site and users can click through them to travel through the cave as you would in real life.

There are also sound effects, such as the river, that he recorded in the cave.

You can also take the wrong way and have to turn back or end up looping back on yourself, he explained.

The site has been running for five years and Mr Collings-Wells said 13,000 visitors have taken the tour.

He said: "I get experienced cavers who are living in US saying 'I was there in 1970s', people who have never been caving and school kids using it part of geography project."