Carcassonne is a cool place.
We got to stay in one of the only 2 hotels within the walls of the old city. We just fell on this one because we booked it before leaving Avignon in the afternoon. We got to Carcassonne on dusk and had no idea where we were going. It was such a fun opportunity to walk outside our front door and be in the mix.
If any of my friends were to visit, I would recommend staying in one of the the 2 hotels or the one right outside of the main gate to take advantage of the old city. There is a different vibe at night compared to the rush of the daylight hours with the day-visitors.