Well, I went to Antwerp and a day trip to Gent, and I enjoyed myself. If you like art, you can visit Rubenshuis and the Royal Museum of Fine Arts, take a scenic walk along the River Scheldt, or visit Het Steen (a medieval castle which is also Antwerp's oldest building). The Cathedral of Our Lady is also very beautiful, and the Grote Markt is just a stone's throw away. Antwerp is a very walkable city, so I'm sure you'll have a good time exploring it.
Gent is about an hour by train from Antwerp, go walk about the Graslei, pop by St Bavo Cathedral and visit the (creepy) Gravensteen castle.
Have fun!