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. Sporadic local visitations likely continued for many years, but the first formal investigations were in the summer of 1967 by members of the Karst Research Group (from
McMaster University in
Hamilton, Ontario) led by Dr. Derek Ford, following up on a tip from a local outdoorsman. KRG teams penetrated past the cave's first obstacle, an 8m drop, and explored the main trunk passage. 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. The Ice Plug, the 'end' of the cave, was discovered by Mike Boon during a controversial solo trip in the winter of 1970. Soon thereafter cavers helped produce
The Longest Cave, a
National Film Board production, during which some side passages were explored. The first woman to the Ice Plug at the end of Castleguard Cave was Jane Mulkewich. 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 . Such explorations continue today, but with diminishing returns as the major leads have all been checked. 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'. The measured height was to the floor of the top chamber. 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. A Canadian-supported team from the UK dived the sump at Boon's Blunder in 2009 and 2010, reaching substantial dry
phreatic passage after a dive of . Exploration of these passages is expected in the future. Concurrent with exploration was the
survey, or mapping, of the cave. 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. But the prospects of hand-drafting a map seven metres long were daunting, and production was delayed until the arrival of computer technology. After further work on verification, addition of passage detail and survey of various unchecked leads, a final map in digital format was produced late in 2005 and is updated whenever new mapping occurs. == Videos ==