There are two things to do. Visit the great old town and enjoy the beach.
The place also has several nice places to go out dancing at night. Also the open air cinema is a nice place to spend one night.
Quick Tips:
If you want something more then just to lie on the beach, walk a little bit more north to the resort "sunny beach". All popular watersports are available there. Like surfing, the banana and so on.
Best Way To Get Around:
Walking is actually the best way to get around. Alternatively, you can find place to rent a bike. I know there are some places to, but I don't remember the addresses.