Swim-to-work cavers mark 10th anniversary of big job

Waitomo caves.

The 4.5km Ruakuri Cave at Waitomo was reopened 10 years ago this month.

Some of the builders who installed its 15m-deep spiral entranceway and other facilities will gather at Waitomo in October to mark this anniversary.

About 50 cavers tackled the tricky renovation, which followed the cave being closed for 18 years because of a financial dispute.

Ruakuri operations supervisor Angus Stubbs says most of them are still working in adventure tourism in New Zealand or overseas, though probably only about half will be able to attend the reunion.

During the early stages of the work, these men and women had to swim to work in the dark each day.

Wearing wetsuits and clutching waterproof toolbags, they would jump down a subterranean waterfall then ride currents to construction sites in the bowels of the earth.

"They even jumped a concrete mixer over the falls, floating it to about the middle of the 4.5km long, 80m deep system," said Stubbs.

"Our crew wheelbarrowed tonnes of concrete through the cave. They built the suspended walkway amid fragile, protected structures and coped with cold and dark. Being experienced they handled everything well, and injuries were few."

Two streams flow through the cave system, which has several entrances.

Stubbs says part of the fun of going into the Ruakuri systems is coming upon other tourists or adventurers with "whom you did not enter the cave".