Hi Jo-Anne!
I spent my summer holidays in Peņiscola three years ago. My impression was that it was a very quiet city. Peņiscola is quite known in Spain and I thought that it was going to be the tipical summer city with thosands of young people uttlerly drunk on the streets but, to my surprise, it wasn't that way.
But, be careful!
In my opinion, Peņiscola has three different areas. Have you ever seen a photo of Peņíscola?. It's like a big "L". The small part of the "L" is the old city and the castle, and the big part of the "L" is about 8 kilometers long with just one line of flats / houses next to the sea.
The first area is the old city all around the castle. Really really beautiful. The sea, the narrow street without cars, people eating ham and cheese on that narrow streets...
The second area is the first part of the big side of the "L" and I'll call it semi-old area. It is about 1000 meters long. Goes from the old city next to the sea and the beach in this area is wide. It has a beautiful way where people have walks with their childrens. At night is full of street artist painting, or with puppets for the childs or creating figures with the sand of the beach. In this area you'll find all the restaurants, "terrazas", etc and all the parents strolling with the childrens eating whoppy ice-creams.
The third area (the new area) is the next to this paseo and has about 7 kilometers long!. This area goes next to the sea but the beach has only 1 or 2 metros wide (or less). There are loads of stones in the beach and you cannot lie down on the beach. There is almost no restaurant and no bars, just flats one beside the other forming a line of just one flat wide, parallel to the road and to the see. Here there is nothing to do and to reach the interesting area of peņiscola (old zone and semi-old zone) you must have a car (or walk, walk, walk through a too long and narrow way). During the day and sometimes at night this road is full of cars and there are loads of traffic jams because the roads is too narrow and all the people want to go to the "center" of Peņíscola.
Well!. I hope I've explained it well!.
I liked Peņíscola very very much. I spend all nights strolling with my girlfriend through the paseo of the semi-old and through the old area. We never went to the new and ugly and large area.
By the way, if you want "marcha" "fiesta" this is not your city.
Bye