The Victorians loved to decorate everything as though it was a cathedral, no matter how utilitarian it was. Crossness Pumping Station is no exception.
Believe it or not, this is a sewage pump, with giant steam engines designed to pump sewage away from London towards the east, till it reaches the sea, where the contents were discharged into the ocean. You can see the steel pumps on the right of the picture
Here is the same view from the level above:
Here is what it looks like from the outside:
It's in Abbey Wood, South East London and is open to the public for a small fee (about £10).