A group of international cavers left Fernie early Sunday in the hope of finding a new entrance to the deepest cave system in North America, north of Mexico.

Named Bisaro Anima, the cave stretches 5.3 kilometres in length and 670 metres deep, and is located in a mountain plateau northwest of Fernie that is so remote, it can only be accessed by helicopter.

The latest expedition to Mount Bisaro will run for about a week and is being led by Calgary man Christian Stenner and father-and-son team Henry and Jeremy Bruns, who were involved in the initial discovery of the cave entrance in 2012 and further exploration .

It aims to extend the known length and depth of the Bisaro Anima cave, and has been named 鈥渆xpedition of the year鈥� by the Royal Canadian Geographical Society (RCGS).

鈥淚t鈥檚 a bit of excitement and anxiety,鈥� said Stenner as he waited at Ascent Helicopters in Fernie on Sunday.

鈥淲e never know what we鈥檒l discover because we can鈥檛 see what鈥檚 around the corner in a cave, so it鈥檚 always a bit of an adventure to see what we might find, so there鈥檚 excitement in that but also some anxiety because you never really know what you鈥檙e going to be doing.鈥�

The cavers will spend the week exploring previously uncharted passageways in an attempt to find a new entrance to the cave system.

Stenner said there were almost 100 different surface holes, shafts and sinks on the plateau.

鈥淪ome of those may connect to the cave but we just need to find and make those connections,鈥� he said.

鈥淚f we do that, we could even make the cave much longer than it鈥檚 already known or perhaps even deeper if we count that a higher entrance than the known entrance is found.鈥�

The cavers are prepared to stay underground for days at a time and have packed sleeping bags, hammocks and several four-litre tubs of dehydrated meal mix, along with personal items such as a ukulele and harmonica.

Conditions inside the cave will be cool and wet, with the temperature remaining at about 2C year-round.

鈥淲e expect it to be pretty damp underground, so there鈥檚 going to be some waterfalls and water spray, and things, and lots of drips,鈥� said Stenner.

鈥淭here鈥檚 going to be sections that are pretty muddy and there鈥檚 going to be some shafts, and rifts and things that we鈥檙e going to have to negotiate over and, of course, these big, long drops that we have to rappel down and then climb back up to get out of the cave.鈥�

Stenner has 15 years鈥� experience caving in places including Mexico, Central America, Belize and the Pacific Northwest, U.S.

He said Bisaro Anima was different to other systems he had explored.

鈥淚t鈥檚 pretty impressive, these really neat long shafts to rappel down and climb up, and there鈥檚 quite a mix of open passages and tight squeezes,鈥� he said.

As with any outdoor activity, there are risks involved with the expedition, which the cavers have tried to plan for with first aid and rigging equipment.

鈥淭here are risks with rock fall, there are risks with being on rope and sort of the technical aspects, so we鈥檝e recruited a team which is well versed in that and should be able to negotiate those challenges,鈥� said Stenner.

Cavers have travelled from Quebec, California, U.S., Alberta and B.C., for the expedition and their excitement was tangible on Sunday.

For some, it will be their second time exploring Bisaro Anima.

Genairon Jerome took part in last winter鈥檚 groundbreaking expedition when the cave was confirmed as the deepest in Canada and the U.S.

鈥淚t鈥檚 hard to be in the cave, so I was tired and 鈥榦h my god it鈥檚 difficult鈥� but outside鈥� I was very happy to break the record and to be alive,鈥� he said.

The Montreal-based Frenchman hopes to set a new record during this expedition and will be better prepared this time with warm clothing, and waterproof writing materials for surveying.

鈥淚 am very happy to be here for a second time,鈥� he said.

鈥淚 hope to find another entrance in the plateau.鈥�

An expedition of this size can costs tens of thousands of dollars and Stenner said the group was fortunate to receive funding and equipment from the RCGS and Mountain Equipment Co-op.

He is already planning to return to Bisaro Anima later this year to explore more leads and a sump (underwater passage) at the bottom of the cave.

鈥淎 caving project is not measured in one expedition, it鈥檚 measured in years and it can be dozens of years, so the potential for this exploration project to go on for many years is pretty great,鈥� he said.

鈥淲e have people from all around the world that may come to go caving and it鈥檚 kind of, I guess, a unique thing for Fernie to be sort of home to this deepest cave north of Mexico and deepest in Canada, and pays homage to Mt. Bisaro and the history of Mt. Bisaro.鈥�

The mountain range was named after Fernie-born infantryman Torindo Bisaro, who fell during the invasion of Normandy in World War II, with some underground passages dubbed Vimy Ridge, the trenches, Dieppe and the Black Watch.

For English caver Mark Scott, this week鈥檚 expedition will be his first time alpine caving in Canada.

He lives in San Francisco, California, and was invited to join by Jeremy, whom he met several years ago.

鈥淚t sounds like a really fun, interesting system with a good potential for significant depth records,鈥� he said.

Scott has been involved in discoveries in other parts of the world and said it was a sense of exploration that drives him to cave.

鈥淯nless you can convince someone to go into space or you like exploring deep oceans in submarines, there are very few places on earth you can go to that no person has ever been to before,鈥� he said.

鈥淐aves are, for someone who is not doing it professionally, 100 per cent of the time, about the only frontier left where you can actually go find something new, that鈥檚 new to mankind, that no one has ever seen.鈥�