Guests visiting the main sanctuary of the Cathedral of the Incarnation in Garden City can be forgiven for gaping upward like awestruck tourists.

The ceiling, held in place by flying buttresses like cathedrals in Paris and Rome, is meant to inspire the same sense of awe today as it did in the Long Islanders who first worshipped there more than 130 years ago.

“The cathedral is meant to be a place where heaven meets Earth,” says the Very Rev. Michael Sniffen, dean of the Cathedral as well as a guide for what is perhaps Long Island’s most unusual historic tour.

Although the cathedral is the seat of the Episcopal diocese, covering Long Island, Brooklyn and Queens, you don’t have to be among the 900-member congregation to take the tour. Anyone can join Sniffen for a walk through Long Island’s past featuring museum-quality artifacts, secret passageways and — like many a hallowed historic site — a spooky legend.

THE BACK STORY

Garden City wasn’t originally meant to have a cathedral, Sniffen said on a recent afternoon tour. After Garden City founder Alexander T. Stewart died in 1876, his widow, Cornelia Clinch Stewart, decided to build a cathedral in his memory. The more than 200-foot-tall brown sandstone edifice, completed eight years later and consecrated in 1885, was then the tallest building on Long Island, Sniffen says.

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The Gothic Revival style, reminiscent of 14th century cathedrals, features gargoyles on the exterior. “The downspouts are all faces, and the water comes out of their mouths,” Sniffen says, leading guests into the sanctuary through an ornately carved — and recently refurbished — wooden door.

CENTENNIAL BELLS

Inside the sanctuary, which has enough seating for 600 people, the inlaid-marble floors are polished brightly. They are inlaid with coats of arms of the Irish immigrant Stewart, his wife and other notables. To the right of the front door, a spiral staircase leads to the top of the cathedral tower. The tower bells originally were cast for the 1876 U.S. Centennial in Philadelphia and brought here by train.

Everywhere you look, you’ll see treasures. The British-made stained-glass windows on both sides of the sanctuary depict the incarnation of Jesus Christ — the biblical passages for which the cathedral is named. The ceiling is elaborately carved and painted in gold leaf. The cathedral’s Casavant Fréres organ is only 30 years old, but it includes pipes from the original 1885 instrument.

“It’s the largest pipe organ on Long Island,” says organist Larry Tremsky of Garden City. You may want to cover your ears if Tremsky plays a few “Phantom of the Opera”-loud notes.

A SECRET PASSAGE

What would a cathedral be without a hidden passageway? Priests who want to take a shortcut can climb another set of winding iron stairs from the clergy vestry to the upper sanctuary.

Downstairs, in the undercroft, congregants gather for coffee after Sunday services. A casement displays some of the cathedral’s treasures, such as a bishop’s amethyst ring, and a gold crosier, a hooked staff carried by a bishop as a symbol of pastoral office.

“It’s museum quality, but the great thing is, it’s still in use,” Sniffen says of the crosier.

TALES FROM THE CRYPT

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Downstairs in the Crypt Chapel, also known as the Chapel of the Resurrection, is the final resting place of a number of bishops as well as the Stewarts. And thereby hangs a ghostly rumor.

After A.T. Stewart’s death, grave robbers stole his body from where it was interred in the Bowery in Manhattan. His wife reportedly ransomed Stewart’s remains for $20,000. They are both said to be buried in unmarked graves under the Crypt Chapel altar, although there are doubts.

“It’s one of those stories — who’s buried in Stewart’s grave?” Sniffen says, adding: “The story goes that if anyone tampered with the grave, it was booby-trapped, so the bells in the tower would ring.”

So far, where the Stewarts are concerned, those bells have remained silent.