The market is called Ayothaya (อโยธยา) which is the old name of Ayutthaya(อยุธยา). It is located outside the old city wall, situated close to Mahaeyong Temple and next to Ayothaya Elephant Camp. This great Thai market makes an excellent day trip.
The main part of the market is alongside a waterway surrounded by classic Thai-style stilt houses. There are about 50 boats on the lake selling food and drinks, and about 200 shops are in the market. Overall, the feel of the place is quite touristy with all the usual gift items, however it does have a genuin Thai feel to it with regards food and ambience.
You will find several boat noodles stores here since Ayutthaya is famous for it. There are also plenty of river prawns and sea food available. Oh! and of course Roti Sai Mai (โรตีสายไหม) or Thai style cotton candy which is the signature sweet of Ayutthaya.
If you like Thai massage, there are several riverside places available including a fish spa to relax your feet after a long walk.
What I like about this place is there are short 20minute boat tours available so you can see the atmosphere around the market. It costs only 20 Baht per person for both Thai and foreigners