If you can get to Utrecht on Sunday afternoon (26 August) and you like mussels, head to Lucasbolwerk (over by the Stadsschouwburg) for the second Mosselfestival. The cafés in the area (De Potdeksel, Tilt, De Stad, and Zocher) are hosting an outdoor festival with Zeeuwse mussels, and local wine and beer. A good-size portion of mussels costs just €3.50.
We went last year and were very impressed with how nicely the mussels were cooked, with a perfect blend of seasoning. De Leckere beer will also be on hand again, so you can probably drink a Wittevrouwen bier next to Wittevrouwenstraat.
The event starts at noon and Utrecht writer Jerry Goossens will officially open the festival at 14:00. The event lasts until approximately 20:00. There will also be a bouncy castle for the kids to play. You can find more information at utrechtsmosselfestival.nl. Hopefully the weather will cooperate!