I drove to northern Manchester one sunny morning with drains in mind. Redbarn still sports a large metal grille that resists casual entry, so headed to nearby Foxdenton. The infall stands proud and makes little effort to conceal itself, it's grille reduced to lying in the water creating a mini dam. Shortly after you leave the sun behind you it returns through an open manhole.
A small chamber housed a junction with a sidepipe and a manhole shaft, pretty much the biggest open space in the culvert. After this was a walk punctuated with only a few sidepipes and manhole shafts that looked more cave like than usual ones.
After a while the water started getting deeper and the thundering sound became louder. Several walkable sidepipes lead off before this, one out to an outdoor pool, another upto some stairs with a grilled top, probably overflows for the works.
I waded through the foam that smelt less sewer and more fresh than the average sewer aroma. Around the corner was a large channel of post-treatment sewage works output, it had real power behind it so marked the end of the explore. I had no appreciation of quite how much output a works produces, even a relatively small one like this. Modern day treatment is pretty impressive.