Conspiracy theorists believe that Rosslyn, with its suspected vast, sealed underground vault, is the resting place of the world's most elusive icons - the Holy Grail, the Ark of the Covenant, scrolls of early Gospels, fragments of the crucifixion cross, even the mummified head of Christ. Experts call the chapel the "Bible in stone," its lavish, symbolic carvings a code waiting to be cracked.

Rosslyn certainly has a whiff of the other­worldly about it. Some say it rests on ley-lines - imaginary straight lines connecting ancient sites - that lead to Stonehenge and other sacred sites. Many think it is haunted. Staff hear children's voices echoing through the sacristy when the chapel is empty. Visitors have seen a phantom monk shuffling across the floor or kneeling to pray at one of the altars. Psychics, clairvoyants, and ghost hunters are always nosing about.

With its dim lighting and smell of ancient masonry, Rosslyn can send a shiver through the most hardened skeptic. Everywhere you look there is a riddle rendered in stone.

Although finished by 1492, the chapel contains carvings that resemble American plants, such as maize and cactus, which begs the question: Did the Templars journey to the New World before Columbus?

Another enduring puzzle is the vaulted archway at the east end of the chapel. In The Da Vinci Code, Sophie, the cryptographer, has an epiphany while gazing up at the forest of small, elaborately carved boxes that jut from the ceiling. Some think the pattern they make contains the encoded notes for a piece of music. Legend has it that anyone who deciphers and plays the tune will be shown the "treasure" of Rosslyn. On the day I visited, a young man from Florida was staring intently at the ceiling, a well-thumbed copy of The Da Vinci Code in his hand.

"You can really feel this place is hiding something," he whispered. "It's just a matter of figuring it out."