One of my cats had to be kept separate to the others for a while due to medical treatment (mainly so it didn't go outside via the cat flap).
She stayed in our study which we weren't using much at the time and had a litter tray which she appeared to be using as normal.
However, it turned out that she'd also had a wee under the study desk and it took us a couple of days to realise.
We cleaned it up from our floor which is practically brand new and expensive Amtico.
All the smell is gone but it's left a kind of white bloom which I can't get rid of 
So far I've tried normal floor cleaner, white vinegar and one of those 'animal wee' cleaners that have enzymes in.
Any other ideas?