A Disney YouTuber solved a 15-year-old riddle hidden inside Disneyland, thanks to his subscribers.

Chris Provost, who runs the Provost Park Pass YouTube channel, explained the mystery behind the hidden message and why it hadn’t been solved in over a decade.

During a previous video Provost recorded, fans noticed a unique skeleton painting on the walls of Pirate’s Lair at Disneyland.

The YouTuber incorrectly stated that the picture represented the number of people killed by pirates. However, fans found that the stencil was a semaphore, or a type of code, like the one used in “The Adventure of the Dancing Men,” a Sherlock Holmes story.

The code spelled out the message, “Each answer be havin’ three identical letters.”

Provost began a quest to find the riddles that correlated with the mysterious code; however quickly found one riddle was located in “Dead Man’s Grotto” on Pirate’s Lair, which is currently closed to the public.

The others were never created.

Luckily, Provost’s old footage of “Dead Man’s Grotto” showed where one hidden riddle was and how guests could locate them in the parks.

The answer to the mysterious riddle was bubbles.

While the initial code calls for three riddles to be located, Provost speculated that Walt Disney Imagineers, cast members responsible for creating the rides and attractions at Disney Parks, planned to add more during the island’s refurbishment in 2007.

However, the other two riddles didn’t make the final design.

The YouTuber also pointed out that Imagineers, who were fans of Holmes, put a silhouette of the fictional detective in Mr. Toad’s Wild Ride in Fantasyland.