We are remodeling a 60-year old home where the hardwood floors, hidden all this time under carpeting, look fairly good except for several corners where a cat has been urinating on them over a long period of time.They are dark and the odor is very strong. What is your best advice to eliminate this problem?
Thank you.

Those urine stained boards will need to be cut out and replaced. I have seen some "chemicals" that supposedly remove the odor and some claim bleaching with oxilic (sp) acid will remove the stains but I have never had success with that. Easier and faster for me to remove and replace. And it is sure fire. Not just hoping it will work.

Kill the cat.

Then replace the wood.

If you can smell it now, you may even need to replace some subfloor, or at least allow it to dry.