We just discovered of what might be the largest cave in Canada just last year: https://www.cbc.ca/news/canada/british-columbia/new-cave-bc-canadas-biggest-cave-

We just discovered of what might be the largest cave in Canada just last year: https://www.cbc.ca/news/canada/british-columbia/new-cave-bc-canadas-biggest-cave-1.4929918 https://www.cbc.ca/news/canada/british-columbia/new-cave-bc-... There's a lot of surface that are covered by glaciers or forest and not visible from the sky.