Ontario is home to world's largest artificial underground cavity 2km below surface

There's a little secret hidden deep beneath Northern Ontario, and it comes in the form of what might be one of the strangest science labs on Earth: the Sudbury Neutrino Observatory.

Built more than two kilometres (6,800 feet) underground inside a working mine near Sudbury, the observatory was once used by scientists to study neutrinos — tiny particles from space that are famously difficult to detect.

The underground chamber is considered the largest human-made cavity of its kind, this far below the Earth's surface, with the massive space, roughly the height of a 10-storey building, carved directly into solid rock.

Scientists built the observatory underground because neutrinos are incredibly hard to spot. These microscopic particles are constantly flying through the universe — and through our bodies — but they almost never interact with anything. So, in an effort to catch them in action, researchers had to think far outside the box.

The underground lab, shielded from light and other external disturbances, blocked interference from cosmic rays and background radiation that could disrupt experiments.

And of course, the setup was just as interesting as the experiment itself.

Inside the chamber sat a giant spherical detector surrounded by thousands of light sensors. At its centre was a huge, clear acrylic container filled with heavy water, a special type of water used to help detect neutrinos when they collided with atoms. Even with all that technology, researchers recorded only a handful of neutrino interactions each day.

The observatory took nearly a decade to build, with construction starting in 1990, and the first experiment officially taking place in 1999. The project gained international recognition after helping scientists prove that neutrinos can change form while travelling through space, a breakthrough that, in 2015, contributed to Canadian physicist Arthur B. McDonald receiving the Nobel Prize in Physics.

While the observatory no longer operates in its original form, the underground facility has since evolved into new experiments through SNOLAB, one of the world's leading underground science laboratories.

The observatory isn't typically open for public tours, but visitors in the Sudbury area can still learn more about the project through exhibits at Science North, a popular museum located at 100 Ramsey Lake, in Greater Sudbury, Ont.