Paid parking near castle in the heart of the old city. It was okay for 6m long , 3m high camper. We paid 12tl for a night stay. There is an info point and Bazar right across the street, which was a little bit tricky to go out the other day, because of trucks loading the shops but people are helpful and everything was fine. Don't panic if in the morning there are cars parked in front of you - parking guards have keys and move them. Guards are not available during the night - so late check-in and early check-out could be a problem. We arrived around 9:30 PM. On the other side of the castle there is a hammam which we visited and it was real authentic experience. Free toilets are available at the castle entrance on the left. Down the same street we visited a nice restaurant, serving beer. Gaziantep is one of our favorites during our Turkey trip.