I am assuming it's not carpeted because you said it was swept and mopped. A few years back I moved into an appartment with hard wood floors. The place REEKED of cat pee, in the WORST possible way. I sprinkled baking soda all over the floor, and let it sit there for like 3 hours. Then I used a water vinegar solution and mopped the floors. It made a weird milky like texture on the floors, so I let that dry and used a specific solution for getting out pet odor, any enzyme cleaner will do, and re- mopped. Couldn't smell the cat pee ever again.
Now for carpet, the best thing is to rent one of those industrial carpet cleaners for like $30 from the Sobey's or Super Store and steam clean your carpets. But if that's not in the budget, the baking soda trick will work here too. Sprinkle, let it sit for a few hours, even over night if you can, vacuum and repeat if necessary.