It took an extra week to get to cleaning the pig pen after I caught a cold.
They do try to take care of it themselves, if they have everything else they need.
When the guinea pigs are soiling different parts of their pen, they start dragging hay around the pig pen and lay it down over the dirty areas, and then they just live on top of that and go eat more of the new hay you put out.
I collected almost a half a trash bag full of hay this evening from the 2×6 grid pen they live in.
Husbandry. Guinea pigs know husbandry.