I live in Belgium and here mussels are one of the typical dishes. I might ad it is THE dish. In fact I had some this weekend.
Mussels that don't open, mean they are bad. I remember telling my father this once and he is so stubborn he went on and opened it. (It took him quite some time, though. They seem to be sealed) When he finally got it open, the mussel looked black and it stinked! So I guess it's nature's way of saying don't eat that, it's rotten.
Here in Belgium they boil them in water or broth and add different kids of spices. I had mine marinated in white wine. My father in law ate some provençale and the menu offered spicy and garlic ones. As soon as they are cooked (it takes about 5-7 minutes for them to open in boiling water), they are served with french fries on the side. By the way french fries are actual belgian. But when these were invented, Belgium was still part of France. Belgians have found a nice simple way to eat mussels without having to struggle with a fork. You take your first shell and using your fork take out the mussel and then use this shell to eat the rest of your mussels. Its like a clasp and works perfectly.
I also love cooking mussels and serving them over linguini. This is in fact a typical Italian dish. You marinate them in some tomato and garlic sauce or simply with butter and fresh herbs and serve them over a bed of linguini. Add some fresh parmesan cheese. MMMMMMMMM I'm getting quite hungry now!