It was not actually as cool as I had hoped in that all the old brickwork is up the dangerous channel (the way we didn't go) so it was basically just a really long, filthy culvert, and the river was foul, but I now know an awful lot about buried rivers. I am your go-to girl for telling detail about storm sewers on an epic scale. (I got most of the details right--I had interviewed people who'd done the trip, but I wish I'd managed to mention the smell. And the traffic noise under the highway. Oh well, they were a little distracted.)
We had to portage a whole bunch, too. I kind of feel like I've had my workout for the day.