Castleguard Cave

The classic trip, from the entrance to the Ice Plug by the shortest route, traverses 9 km (6 mi) of cave passage.

Undoubtedly the cave was known to natives throughout prehistory, but the first recorded visit was by Cecil Smith, an outfitter rounding up stray horses during a guided trip to Castleguard Meadows in 1921.

Smith's client happened to be the head of the U.S. Geological Survey, and three years later the cave entrance was revisited and photographed as part of an article on the Columbia Icefield for National Geographic magazine.

After Peter Thompson and Mike Boon were trapped in the cave by sudden flooding near the entrance, explorations were limited to mid or late winter, with attendant difficulties.

Soon thereafter cavers helped produce The Longest Cave, a National Film Board production, during which some side passages were explored.

Explorations slowed somewhat following national park access restrictions, but picked up again in the 1980s when most of the major side passages (including Boulevard du Quebec and extensions to Thompson's Terror) were explored by Canadian and international teams, bringing Castleguard Cave to a known length that exceeds 20 kilometres (12 mi).

In 2005, a Norwegian group spent three days bolt-climbing the '200-foot aven', a vertical shaft going straight up from the cave level about halfway in, slightly inside of the site known as 'Camp One'.

Somewhat to the disappointment of the explorers the chamber narrows to an impassable crack; however, in caving first impressions are not always authoritative and there is still some hope of further penetration in that area.

Data was held at a number of sources, and doubts about completeness or consistency of standards led to a remapping project coordinated by Steve Worthington and supported by cave radio location work by Ian Drummond.