Seaside Toldboden is a collection of restaurants (I'd say a step more upscale than a food hall, but they are all housed under one roof) located near Kastellet and the Little Mermaid. In the summer, it's a nice place to grab food or a drink and sit outside. Personally I wouldn't make a trip here specifically for the food, but if you are in this area to see the sights, it's a good option for food!