A huge tunnel has opened below Niagara Falls

A whitewater wonder visited by everyone from Marilyn Monroe to Mark Twain, Niagara Falls has been a magnet drawing global travelers for at least two centuries. But until this year, a huge tunnel buried deep below the cascade has been off-limits to visitors.

The rocks beneath the gigantic triple waterfall that straddles the border between the US state of New York and Canada’s province of Ontario are honeycombed with chambers carved out to harness the powerful forces of nature thundering overhead.