This is the the network of pipes right below the combination boiler, which does both jobs of heating the water for the central heating (which goes upstairs and downstairs) and also the hot water (which also goes upstairs and downstairs).
It looks a bit extra complicated because of the washing machine and outside tap attachments.
They cross over etc partly because it's an old house (70 years or so) and has been updated at various points in its life.
Awesome job there Scawen.
BTW, the next time you have a stuck tap, or bolt, try a product called PB Blaster instead of WD-40 (if you can get it where you live). It works much better and much faster.