Zorra invites foodbloggers around the globe to celebrate this year's Onion Day. I had never heard of the annual Zibelemärit in Berne (Switzerland) before but it sounds interesting.
There's a traditional Onion Market in Germany as well: It is called Zwiebelmarkt and takes place every second weekend in October. The market is held in Weimar, and it is said to be the only market fair that has continuously taken place since the Middle Ages and that is a typical regional folk festival.
For me, both Berne and Weimar are great places to visit - whether there is a Onion Market taking place or not. :-)
One of my favourite dishes containing onions is a Chinese dish called 洋葱牛肉 ("yáng cōng niúròu" in pinyin). This actually means onions and beef and you can get it in many restaurants in China, though I think it is a Northern Chinese dish as they used to have more beef in the North.
It is easy to prepare: Actually just cut onions and beef into small slices and stir-fry them. I like the combination of these two ingredients very much.
Such dishes seem to exist around the world: There is a Swabian "Zwiebelrostbraten" that has a similar flavour but of course the beef is not chopped but prepared as a whole piece of meat.