The Ojibwe tell of Nanabijou, a powerful spirit who protected the silver deposits hidden beneath the waters near Thunder Bay. He shared the secret of a vast silver mine with the Ojibwe people, warning them that if outsiders ever learned of its location, he would be turned to stone. When a Sioux scout discovered the mine's whereabouts and the secret reached European ears, Nanabijou's punishment was swift: a violent storm rose on the lake, and the great spirit was petrified, his massive form becoming the mesa and cuesta formations that define the Sibley Peninsula today. The legend carries a weight that geology alone cannot, binding the landscape to a story of trust betrayed and consequences made permanent in rock.

The Sleeping Giant's dramatic profile is the result of billion-year-old geological forces. The western half of the Sibley Peninsula is dominated by highlands composed of diabase, an intrusive igneous rock that formed when molten magma pushed between layers of older sedimentary stone. A massive diabase sill caps the upper portion of the Sleeping Giant formation, while diabase dikes cut vertically through the sedimentary bedrock. The underlying sedimentary rocks strike northeast and dip toward the southwest, creating the tilted cuesta formations that give the reclining figure its shape. The eastern half of the peninsula drops to lowlands, a contrast that makes the western cliffs all the more imposing when viewed from the lake or from Thunder Bay's skyline.

Lake Superior's cold, moderating influence creates microclimates across the peninsula that support species found nowhere else in southern Ontario. The park shelters 23 species of orchids, including the small round-leaved orchid, one of Ontario's rarest plants. Twenty-two species of alpine arctic disjuncts, plants typically found in tundra or high mountain environments, survive here as relics of the last ice age, clinging to the cool, moist conditions that Lake Superior provides. Nearly 200 bird species have been recorded in the park, with about 75 known to nest here. The Thunder Cape Bird Observatory, located at the peninsula's tip, monitors the migration patterns of species that use the peninsula as a flyway corridor over the open lake.

The Kabeyun Trail runs roughly 40 kilometres along the western shore of the peninsula, threading through old-growth boreal forest and emerging at clifftop lookouts with views across Lake Superior. It is the park's longest and most celebrated route, though the network extends to over 100 kilometres of trails in total. The Top of the Giant trail leads hikers to the highest point on the formation, where the view encompasses the open lake, Black Bay to the east, and Thunder Bay's harbour to the west. The park established in 1944 as Sibley Provincial Park, renamed in 1988 to reflect the formation that defines it, offers year-round access: summer brings guided nature walks, campfires at the amphitheatre, and boating on Marie Louise Lake, while winter opens groomed cross-country ski trails through the silent boreal forest.

The park's visitor centre at Marie Louise Lake campground anchors the Natural Heritage Education program, weaving together the threads that make this peninsula singular: the geology of the Sleeping Giant formation, the Ojibwe legend of Nanabijou, the botanical rarities, and the history of the Silver Islet mine at the peninsula's southern tip. That mine, which pulled $3.25 million in silver from beneath Lake Superior before flooding in 1884, is part of the same geological story, its ore deposited by the same ancient forces that built the Giant's profile. The seasonal community of Silver Islet, where miners' houses now serve as summer cottages, sits just outside the park's southern boundary. With more than 240 campsites, boat ramps, rental canoes and kayaks, and the Lake Superior National Marine Conservation Area along its eastern edge, the park is both a recreational destination and a place where deep time, indigenous tradition, and industrial ambition converge on a single peninsula.