Koen Van Weel / Pool via Reuters

Crown Prince Willem-Alexander of the Netherlands participates in a toilet-bowl-throwing contest in Rhenen on April 30, 2012. The royal family celebrates the annual Queen's Day on April 30.

Robin Van Lonkhuijsen / United Photos via Reuters

Queen Beatrix of the Netherlands waves to well-wishers in Rhenen on April 30, 2012.

Hordes of orange-clad revelers took to the streets of towns and cities across the Netherlands on Monday to celebrate Queen's Day, a public holiday that marks the official birthday of Queen Beatrix.

Members of the royal family traveled to the town of Rhenen to join in the fun, with Crown Prince Willem-Alexander making a particular splash. The heir to the throne eagerly put himself forward for a series of challenges, culminating in a popular local pastime: the toilet-bowl-tossing contest.

According to the blog Sanitation Updates, the prince attributed his not-inconsiderable aptitude for the sport to his chairmanship of UNSGAB, the United Nations Secretary-General's Advisory Board on Water and Sanitation.

The contest brings to mind the the exploits of those members of the British royal family who took part in It's A Royal Knockout, a bizarre TV game show fondly recalled as "the day when royalty lost the plot."

Compared to the recently-disclosed leisure activities of another European monarch, Spain's King Juan Carlos, though, it seems positively harmless.

Koen Van Weel / Pool via Reuters

Princess Maxima and Crown Prince Willem-Alexander participate in the traditional tug-of-war event in Rhenen on April 30, 2012.

Jasper Juinen / Getty Images

Spectators wave to Queen Beatrix from a window in Rhenen.

Robin Utrecht / EPA

Queen Beatrix doing a painting during her visit to Rhenen. The Queen's Day tradition started on 31 August 1885, on the birthday of Princess Wilhelmina, later Queen Wilhelmina.

Robin Utrecht / AFP - Getty Images

Princess Annette, left, and Princess Maxima participate in a soapbox race in Rhenen.

Follow @msnbc_pictures