Gah it was minging. Well nothing very terrible, except lots and lots of dust.
In theory I move the beds every so often - big clean upstairs is on a Sunday and moving a bed to clean behind it is on the rota of things to do then - like moving DS1's chest of drawers etc.
But it looked like it was months since I had done it. Oh dear.
Anyone else such a slattern? Or do you "do" under your beds every week or two?
(should add that it's also packed out with clothes we are not using atm (eg too small for DS1, too big for DS2) so it's not the easiet job, but still am shocked at own slatternliness)