Always celebrated on January 2.
This day is a public holiday in the following cantons: Aargau, Bern, Fribourg, Glarus, Jura, Lucerne, Neuchâtel, Obwalden, Schaffhausen, Solothurn, Thurgau, Vaud, Zug and Zurich.
Berchtold's Day ('Berchtoldstag') commemorates Duke Berchtold V of Zähringen (d. 1218), who founded Bern, the capital of Switzerland, in the twelfth-century.
According to legend, he left on a hunt declaring he would name his fledgling city after the first animal he killed. The hunting trip was a success and the Duke managed to kill a bear, or Bern in German.
Despite many references to the day as St. Berchtold's day, he wasn't a saint (certainly not to bears anyway). We are just so used to holidays in Europe being named after saints, that many people have automatically canonised the Duke.
Handily placed in the calendar, by the ever practical Swiss, to give an extra day to enjoy or recover from the New Year's celebrations, Berchtold's Day is a light-hearted, family orientated celebration.
Though it's hard to see the immediate connection with killing a Bear, nuts form a large part of the celebration. Perhaps an explanation is that the Duke managed to kill a Squirrel rather than a Bear, and his exploits have become exaggerated during the intervening centuries?
Eating nuts and nut games, followed by singing and folk dancing are features of Berchtold Day gatherings.
Traditionally children will begin to hoard supplies of nuts in early autumn for Berchtold's Day, when they have a "nut feast".
One favourite game of the children is to try and make "hocks." You need five nuts make a hock - four nuts placed close together, with a fifth placed on top. This is seemingly simple feat of nut engineering is surprisingly difficult to construct and maintain.
Though the author favours the Squirrel theory and would endorse the immediate re-naming of Berne as 'Eichkätzchen Stadt' (Squirrel Town); the nut element, like most holiday traditions, was most likely appropriated from a much older winter custom, when food such as nuts stored from the autumn harvest, would have been treats eaten to celebrate the turning of the seasons and that spring was now closer than Autumn.