Each year since 1999, the Vanderbilt Museum in Centerport has hosted sold-out 30-minute guided twilight tours on select evenings in December — offering a rare night view into the Vanderbilts’ 24-room Spanish revival mansion outfitted with holiday adornments by local designers, decorators and garden clubs.

The 2016 tours will take place 7 to 9 p.m. Dec. 26 and 27. It is the only time of year when visitors can see the private living quarters at night. Daytime guided tours also are offered through the holiday season.

Mary Schlotter, who has volunteered her decorating services at the museum the past several holiday seasons, says she draws on history for inspiration.

“I like to keep in mind, would the Vanderbilts be pleased with what we are creating there?” says Schlotter, owner of Centerport-based Harbor Homestead & Co.

This year, that’s a dress form resembling a lavish storefront mannequin with a full skirt of pine tree branches stationed in the dressing room of William K. Vanderbilt II’s wife, Rosamund.

TAKING A CUE FROM HISTORY

advertisement | advertise on newsday

“My inspiration came from the dress form that was in Mrs. Vanderbilt’s dressing room. I envisioned her getting ready for a holiday party, wearing a beautiful evening dress, perhaps listening to [singer] Jo Stafford as she dressed,” says Schlotter, 62, of Centerport.

The museum, which is on the National Register of Historic Places, prohibits the use of fresh greens to create the skirt on her dress form, Schlotter says, due to fire and other hazards.

The restriction created a bit of a challenge, says Schlotter, She spent several days offsite constructing a chicken wire frame around the form, then wrapped the skirt in two layers of various artificial greens purchased from a craft store to drape in a realistic fashion.

Schlotter factored the room colors into her design: The champagne-colored walls, the chandelier crystals that hang on the sconces and the aqua accents. She tapped designer Lorri Sue Kessler-Toth of Couture Creations in Huntington Bay, who has worked for Vera Wang and Carolina Herrera, to sew a blue velvet cover for the dress form.

All told, the creation took about 12 hours of labor, Schlotter says. This is just one example of the amount of precision and talent devoted to the tours each holiday season, according to Stephanie Gress, director of curatorial affairs for the Suffolk County site.

AROUND THE MANSION

The Vanderbilt Museum is almost entirely as it once was, through the preservation efforts of Gress and her colleagues. All but one room appears just as it was when it was last inhabited by a family member in the early 1940s.

Tours showcase the antique furnishings in the family and guest rooms and a dining room with centuries-old furnishings from a Spanish monastery including fine china, crystal and dinnerware.

advertisement | advertise on newsday

Organizers expect as many as 600 guests over the two-night evening tour schedule alone.

With as much that has been left behind in the lavish living spaces, Gress says she hopes visitors come away with a sense of what the Vanderbilt family was really like and how they came to amass their wealth.

Says Gress, “as far as rich people go, they were very hardworking, accomplished and industrious people.”