If you are looking for a restaurant in a unique location, Vessel11 in the Wijnhaven is definitely recommended. The restaurant is actually a boat docked in the centre of Rotterdam.
They have a nice terrace on their deck, where you can enjoy a drink and snack on a sunny day in Rotterdam. But also on shore next to the boat they have tables where you can take a seat and enjoy the sun. But you are also in the right place on rainy days. In the back of the boat you are dry because of the roof.
Vessel11’s menu is inspired by British cuisine, with a seasonal and modern twist. In addition, V11 often organizes live music events, with fun (up and coming) bands and musicians. This way you can enjoy a live show after (or during) an evening of drinks!