Another for Italy here!
Rome if it's a short visit as so easy to get to and you can walk the city easily. Lots to do, fabulous back streets, less bustling than the summer. Hotels and restaurants to suit every budget. No need for a car.
If you want to travel a bit more I'd go further south to Puglia and Basilicata.
Spend a few days in Matera and visit the rupestrian churches - maybe stay in a cave hotel - then go over to Paestum where there are THREE fabulous ancient Greek temples and a great museum (and the best mozzarella ever).
Italy is fabulous.
Have a lovely celebratory time.