Ontario's largest cave system is a half-billion years old and reopens this month

Ontario nature lovers rejoice, because the province's largest cave system, the Bonnechere Caves, is almost ready to welcome visitors underground once again for the season.

Located in the Ottawa Valley — home to breathtaking natural trails — and along the Bonnechere River, the caves will reopen over the May long weekend, giving people another chance to explore the sprawling subterranean site, estimated to be around 500 million years old.

The Bonnechere Caves have operated as a tourist attraction for more than 65 years, serving as a popular annual destination for outdoor adventurers during the spring and summer months.

Visitors can take a guided tour through the underground passageways and learn about the cave system's origins, dating back to a time when the region was covered by a tropical sea hundreds of millions of years ago. The ancient body of water left behind marine fossils embedded throughout the rock formations, including coral and other "remnants of prehistoric marine life," all of which are now visible to the naked eye. 

Bonnechere Caves

Guests should expect to spend roughly an hour underground, with guided tours taking groups of up to 25 people through the cave passageways.

The attraction's 2026 operating season begins on May 15, with daily tours running throughout the summer before shifting to reduced fall hours after Labour Day. General admission for adults is $25, including taxes and parking fees, and tickets can be purchased directly online.

Bonnechere Caves

Visitors can also make a full-day trip of the experience, as Eganville and the surrounding area are known for museums and scenic biking trails that just may be worth checking out!

The Bonnechere Caves are located at 1247 Fourth Chute Rd. in Eganville, Ont.