Blåkulla is the name of the place in Sweden where witches travel to celebrate their witches’ sabbath. Blå is the Swedish word for blue, and in this sense used as a symbol of dark colours and of darkness in general. There are many theories about where Blåkulla is situated, the two most known examples being the island Blå Jungfrun in Kalmarsund near Öland and the mountain Blåkulla by Marsstrand. These places had to be secluded so that the celebrations could be carried out without any disturbance from the public.
According to folklore the witches travelled to Blåkulla on their broomsticks and this they did on Maundy Thursday every year. In order to prevent broomsticks from being used by a witch at this time of year, people used to hide them. People also used to light fires, close off their chimneys and sometimes fire guns into the air to scare off the witches. To this day you can sometimes see remnants of this when people in Sweden set off their Easter firecrackers.
These days most people do not live in fear of witches anymore, as now we mostly see them in the form of little children dressed up as ”påskkärringar” (witch-like creatures) hunting for candy. In return for the candy the children hand out Easter drawings with Easter greetings on them.
You can find extra information on the Wikipedia page (in Swedish): Blåkulla
 Note from Ed. – Much like the Halloween tradition of trick or treat.