On this day a hundred years ago two brothers, Tommy and Jeff Morgan, decided to explore the cave using candles to light their way and drawing arrows in the sand to mark the way back.
What they discovered was a world of stalactites and stalagmites. On their journey they came across a lake and unable to continue they returned with a fishing boat called a coracle.
Their adventure continued when after they had crossed the first lake, they discovered another three. But like their first visit, their path was too tight to get through and had to give up.
Just over 50 years later, in 1963, a woman called Eileen Davies managed to struggle through it. Lying in wait was over 10 miles of unique cave and it's believed this is just the tip of the iceberg.
100 years after the caves were first found and the descendants of the original cave explorers are still in charge of them.
To mark its centenary, the National Showcaves Centre for Wales has installed a new hydro plant costing over £300,000. According to the centre the plant will make the caves the first 'self sufficient' energy producing attraction in Britain.
An electrical hook to recharge electric cars has also been installed.