Aiguille Creuse is the natural rock formation at Étretat that becomes the destination encoded in one of the messages attributed to Edouard Ingolf. The place’s fame as the secret stronghold in an Arsène Lupin story gives the cipher an alluring literary logic, while the characters’ proposed Templar explanation exposes how readily fascination can be mistaken for proof.

The Peak and Its Fictional Secret

The deciphered message points toward Étretat’s Aiguille Creuse and the nearby Chambre des Demoiselles, naming the hollow peak as the goal of a journey through the landscape. In the account of Lupin’s discovery, the peak is described as a natural castle, habitable within, and as a secret stronghold whose supposed history reaches back to Julius Caesar’s invasion of Gaul and later French kings. It is also presented as the source of Lupin’s immense power.

That imaginative history blurs the line between geography and fiction. The peak’s interior makes it seem like a ready-made vault for hidden knowledge: the setting is real, but the stories attached to it make the place feel like a secret waiting to be recovered.

Ingolf’s Cipher and the Templar Hypothesis

The characters identify the message about the peak by substituting the third letters of Ingolf’s coded words with a second cipher wheel. The decoded French names the Chambre des Demoiselles and the Aiguille Creuse, linking the cipher to the Lupin story in which Arsène Lupin discovers the secret of the hollow peak.

Ingolf is characterized as both a Rosicrucian enthusiast and a devoted Lupin reader. His interest in Lupin’s story helps explain why this particular literary destination appears among the coded messages, without establishing that the message records a medieval secret. The proposed Templar account is explicitly framed as something the group’s Diabolicals could argue: if the Templars knew the peak’s secret, they might claim the message was written at Provins in the fourteenth century. That is a conjecture made possible by the story, not evidence that the Templars actually possessed such knowledge.

Pilgrimage, Interpretation, and Significance

The Lupin story has inspired devoted readers to make pilgrimages to Étretat, search for secret passages, and form anagrams from Maurice Leblanc’s words. Ingolf’s interest belongs to the same pattern of literary fascination, and his cipher reproduces its movement from a fictional mystery to a real landscape treated as though it might disclose hidden history.

Aiguille Creuse therefore functions less as proof of the Plan than as a test of interpretation. The peak’s striking physical possibility, the fictional refuge, and the Templar hypothesis reinforce one another in the characters’ imaginations; their apparent convergence demonstrates how an evocative place can make an elaborate story feel corroborated even when the link remains speculative.