In a remarkable year, two gritty teams of hobbyist cavers are poised to break records for the longest and deepest caves in Canada. With few places on Earth left to discover, caving may be the last remaining activity of true exploration. After discovering a flooded underground chamber, Katie, a daytime accountant, becomes obsessed with returning to the Bisaro Anima cave in the Rockies to push the caving depth record. At the same time, a passionate Vancouver Island team is attempting to link two tunnel systems to create the longest known cave in the country. From abyssal, muddy crawls to heart-pounding, vertical pits and underwater squeezes, these are places where no person has been before. Against a stunning backdrop of natural rock formations, “Subterranean” digs into the oddly fascinating world of cavers to uncover a gripping story of adventure and (if they’re lucky) record-setting discovery.