Bonnechere Caves

The limestone here formed on the floor of a tropical sea around five hundred million years ago, in the Ordovician, and the caves were dissolved out of it later by groundwater. What makes the tour distinctive is the fossils in the walls and ceiling: cephalopods, crinoids, gastropods and corals from a period before fish existed, exposed in cross-section by the dissolving water so they read like a cut specimen. Tom Woodward found the caves in the 1950s, pumped out the water and opened them in 1955; they were and are a family operation. The passages are cool, damp and lit, with a river running through the lower level.

What you actually see

• The wall fossils - Ordovician sea creatures cut in cross-section by the rock.
• The dissolved passages - limestone chambers formed by groundwater.
• The underground river - water still running through the lower level.
• The guided route - a family-run tour explaining the geology and the fossils.

When to go

May to October; the caves close for winter and can flood in spring melt, delaying opening. They hold about ten degrees year-round.

Honest expectations

Closed for winter and opening can be delayed by high water. The tour is guided and timed with limited places. The passages are damp, low in places and cool.

Nearby

Eganville lies east; Algonquin Park is southwest.