I can’t imagine what the smell is like. I know from bitter experience what one cat ‘accident’ with cat urine can do to carpet. Unless you can get to it IMMEDIATELY, it will ruin the carpet and the subfloor. You will never get the smell out....never.
We had inherited tennants from a previous owner, who let their cats pee in the corners of the living room. While Hubby was tearing up the carpet, he would have to hold his breath, pull the carpet a little, then run outside for a breath of fresh air. Then repeat.
Needless to say, we don’t allow pets in our rental units.