The Vanishing Point, a site dedicated to urban exploration and secrets of the built environment, has a page about the massive abandoned Tailrace tunnel at Niagara Falls. (The entire Vanishing Point site is mesmerizing, rich with great writing and fantastic photography.) Part of the decommissioned Toronto Power Co. hydroelectric plant, the tunnel is ten stories underground and only accessible through a hidden slit in the ceiling. From Vanishing Point:
Lying below a river that will relentlessly tear into the bedrock until all has been obliterated from Queenston to Erie, this tunnel thirty-three feet in diameter is imprinted into my being forever. A swirling army of red brick millions strong, the eye of a petrified hurricane leading us right into the centre of the stalled but fighting storm that is Niagara Falls. Standing in its back-blast, in a place far deeper and darker than any middling storm sewer, I breathed and drank from the fount of the universe and swam closer to its centre than I ever will again.