A cave system and popular tourist attraction in the Swansea Valley is celebrating 100 years since it was discovered by farmers.
The Morgan brothers tracked water which was coming onto their land back to a labyrinth of caves on 21 August, 1912.
Three of the caves were later opened up to the public as Dan-yr-Ogof, the National Showcaves Centre For Wales.
As well as attracting tourists, they were used to store art from Cardiff and Swansea in World War II.
Caves director James Price said the thousands of visitors who explore the caves at Pen-y-cae might be unaware of their history.
He said local farmers the Morgan brothers had set out to find the source of the River Llynfell which flowed through and poured out of a mountain on their land, which lies within the Brecon Beacons National Park.
Equipped with candles, a piece of rope and an old revolver - "because they didn't know what they were going to find" - they went into a cave in the mountainside.
"They never found the source of the river, unfortunately, from their point of view," Mr Price said.
"They followed the river in for 30 or so metres until the river took up the whole of the cave floor.
"And I think they were wet enough and they didn't really know where else to go.
"Just holding on their candles they just looked around and saw a little pathway going upwards so literally they scrambled up that and came out into the cave system that we now know is Dan-yr-Ogof."
They discovered limestone caves which are filled with rock formations such as stalactites and stalagmites in an environment which is around 330 million years old.
But the brothers were prevented from penetrating far into the mountain because of a lake.
They later returned with coracle fishing boats and eventually crossed four lakes before being stopped by a small passage that was too small to crawl through.
Mr Price said the farmers' diaries show they actually started charging a very small entrance fee not long afterwards to take people into the caves.
Using candles to light the way, visitors in those early days were expected to wade, and swim through icy cold water, climb underground cliffs, and negotiate huge boulders covered in slimy mud.
The brothers later opened the caves properly to the public in 1939 - only for World War II to start three to four weeks afterwards.
"What happened was the government closed the caves down and actually had two armed guards stand at the cave entrance throughout the entire period of the war," said Mr Price.
He said ammunition was stored in the cave, along with art and documents from Cardiff and Swansea.
Water from the caves was also piped to Swansea when the water mains were damaged by bombs during the blitz on the city.
More to discover
The caves did not reopen to the public until the 1960s because of problems with the country's economy.
But Mr Price said the attraction had been "going strong ever since".
One hundred years on, the caves are still run by descendants of the original cave explorers.
In 1963, a local girl called Eileen Davies, a member of the South Wales Caving Club, eventually managed to crawl through the passage that had stopped the Morgan brothers.
She and others found over 10 miles of caves and cavers believe that there are still more to discover.
"We're very fortunate. Dan-yr-Ogof is unique," added Mr Price.
"It's a fantastic underground environment and that's what the majority of people are coming to see - to appreciate the wonder of nature."