Puerto de la Cruz is the big city in the north of Tenerife. It lies next to the sea and has even a few very small beaches.
The oldtown is okay and there are some nice coffeeshops where you can sit and whatch the passengers go by.
Puerto de la Cruz is in my opinion a good place for a daytrip, but not for living there. I always liked to go there for shopping, a bit walking around …. and then go back home.