That's because they are -- except it's actually a moat around the Tower of London and they're actually walking through an art installation by artist Paul Cummins commemorating the 100th anniversary of World War I.
The British royals visited the landmark on Wednesday along with General Lord Dannatt, the constable of the Tower of London, and "planted" ceramic poppies in Cummins' installation, titled "Blood Swept Lands and Seas of Red."
The sweeping artwork, which currently consists of about 120,000 ceramic poppies, is looking to include 888,246 poppies to represent British and Commonwealth fatalities during the Great War, which lasted from 1914 to 1918.
The artist said he was inspired by a "living will" he found two years prior that used the installation's titular phrase.
"Each one represents someone who died in the First World War from Britain and the Commonwealth. I'm literally trying to represent people because a number is a number, but if you see it all like this it is a visual idea of how many people were there," he said.
The final poppy will be placed on Nov. 11 to mark Armistice Day.
The Duke of Cambridge was heard telling the artist that his piece was "spectacular" before he, his wife and brother joined Cummins to climb the Middle Tower to get a better vantage point on the installation.
On Monday, the royal trio visited Belgium, the invasion of which marked the outbreak of the First World War, and attended a commemoration ceremony at the St. Symphorien Cemetery in St. Symphorien.
The German army had established that cemetery for British and German soldiers who were killed at the Battle of Mons.
William gave a speech honoring the small continental nation and its role in the war. He also addressed the events in Ukraine, which he believes "testify to the fact that instability continues to stalk our continent."
German President Joachim Gauck, British Prime Minister David Cameron, King Philippe of Belgium and Queen Mathilde of Belgium were among the notable leaders who attended the Belgian ceremonies as well.
Meanwhile, Queen Elizabeth II and Prince Charles commemorated the anniversary at different sites in Scotland.
It's been 100 years already. Follow me @NardineSaad.