The River Croal flows through and under Bolton town centre in a series of culverts. They are constructed mainly from stone and concrete and are quite large further upstream. This is where the drains most unique feature is, a bridge next to what remains of a wooden wall across the top of the culvert.
A metal door under the shopping centre gives access to it's foundations.
I'd missed off doing the downstream stretch the first time I'd been so went back with TheVicar to have a look.
We found concrete box culvert and some stretches in the open which had a couple of nice outfalls.