Copied from Wikipedia Queen's Day (Dutch: Koninginnedag) is a celebration in the Netherlands, the Netherlands Antilles, and Aruba on April 30 (or April 29th if the 30th is a Sunday[1]). Originally a celebration of the queen's birthday, it is now mainly known for the 'vrijmarkt' (literally 'freemarket'), the one day in the year that anyone is allowed to sell anything in the streets and 'koninginnenacht' (Queen's Night) on the preceding night. It is also a Dutch holiday.
It started as a celebration of the birthday of Queen Wilhelmina (1880-1962), on August 31. After 1948 Koninginnedag moved to April 30 (the birthday of Queen Juliana). When Queen Beatrix succeeded Juliana on April 30th 1980, she decided to keep the holiday on April 30th as a tribute to her mother. Furthermore, the weather on her own birthday (January 31st) tends to prohibit the traditional outdoor festivities. April 30th, however, is renowned for having very pleasant weather.
During the reign of Queen Juliana, the Queen would welcome people who came to the Soestdijk Palace. The Queen and her family would stand on a dais, and a long line of citizens would walk past, congratulating her and presenting her gifts. These days, Queen Beatrix visits one or two towns where she is shown traditional Dutch dances and demonstrations of old crafts.
This is a typical occasion for oranjegekte (orange craze), when the colour orange is a ubiquitous sight, referring to the name of the Dutch royal family, the House of Orange. There are orange banners, orange colored foods and drinks, and extreme amounts of orange clothing and creative accessories are worn as well. Sometimes even the water in fountains is dyed orange. It is not uncommon for people to impersonate the queen, not always in a flattering manner.
Some impressions of Queen's Day in Arnhem
Another tradition on Queen's Day is the Vrijmarkt. All over the country people sell their most precious family heirlooms

for next to nothing.
It's like a car-boot sale the size of a country. In fact it's the only day when you can sell your stuff at markets like this without a permit, hence the name vrijmarkt (vrij = free, markt = market).
I resisted the urge to buy this lovely basket and believe me it was a struggle but couldn't resist taking a pic of it.