Imagine a tunnel more than ten storeys underground, a hundred years old, bricklined, wet, and completely inaccessible save by descending through a narrow slit in its ceiling thirty feet above the floor, and then returning up the same rope you came down.
Now imagine that this tunnel flows into Niagara Falls, emerging behind the pummeling curtain of water that nearly everyone in North America journeys to see at some point in their lives.
This tunnel exists.
