I found myself with a couple of hours to kill in Wigan so decided to checkout the imaginatively named Wigan Culvert, first seen here.
The Barley brook comes from a 3ft RCP and enters the open briefly before the infall to the culvert proper. The tunnel starts off as a 6ft stone arch, it passes under a railway line then shrinks to 5ft Brick. Some sections require heavy stooping as the floor level varies underfoot.
The last thing I came across before time ran out was a manhole shaft. This had a pipe clipped onto a fitting in the the side of the culvert for pumping something in/out when it's lowered down from the manhole.
I might go back to finish one day but apart from a CSO connection near the outfall I doubt there's much else of interest.