I lived a few years in Calais, and I cannot say that the city center is the best place I've seen. Although there are a few old buildings to look at, most have been wiped out during the war. However, the beach is great, and during the summer I would recommend it. I would even recommend to walk on the beach from Calais to Sangatte.
Food & Restaurants, the l'Aquar'aile is a great restaurant along the beach. It is clearly not the cheapest one but with a wonderful seesight and a great menu it would suit the best "gastronome". If you're lucky enough, you may even see Dover's cliffs from your table.
