Until the 1850’s, Chamber 4 was accessible at certain times of the year, but it had been flooded by the mill leat when the canal and dam were built and nobody had gone any deeper thereafter.
In 1935, Chamber 3 was the furthest place you could reach in the caves on foot. In that year two courageous divers, Graham Balcombe and Penelope “Mossy” Powell, walked along the river bed from Chamber 3 to Chamber 4. Their heavy deep sea diving equipment was not at all suitable for exploring caves.
In spite of this, Balcombe reached Chamber 7 later that year. And in 1948, using oxygen equipment developed during the World War II, he and his colleagues reached Chamber 9.
What makes this chamber so convenient for the divers is a wide curve of mud bank above the green water, big enough for people and supplies to remain dry.
The Cathedral chamber is 30m high, its green water 20m deep, its vast walls red with iron oxide and shining with “flowstone” calcite formations.