Just off Union Square, Hotel G has debuted three ultra-sleek new penthouse suites with stunningly curated furniture and luxurious creature comforts.

Our only question: When can we move in?

Behind the scenes at one of the sexiest boutique hotels in the city, a project had been quietly burgeoning. As it turns out, Hotel G, which opened in 2014, has long been plotting to add more exclusive spaces to its offering of 153 chic guest rooms designed by Hun Aw Studio.

"The penthouses were always meant to be built," says Steve Rizzo, the hotel's GM. "There was a vision to create something very different and unique. Once all of the pieces of the puzzle came together—design, budget, and the dream team to build it—we made it happen."

Guests lucky enough to stay in one of these exclusive new spaces (cost of entry starts at $695 a night) will take the elevator to the 12th floor and then walk up a flight of stairs (hope you're not superstitious!) where two G Terrace suites and the Grande Penthouse suite promise true splendor thanks to Los Angeles-based designer Gulla Jónsdóttir, who started with the already-dapper styling of Hotel G and then seriously pumped up the volume.

Tasked with the goal of creating settings that would feel spacious, sophisticated, and ideal for entertaining, Jónsdóttir took aim at plush European feels—"San Francisco is the most European city in the U.S." she says—loaded with texture and polished details, all rendered in a dramatic palette of black, white, and dove and charcoal gray (described by Jónsdóttir as Italian in essence). She set about carefully crafted juxtapositions, inspired by both the male and female forms as well as by the tall concrete ceilings, skylights, and raw columns that give the 1930s building both a sense of history and a modern edge.

In the Terrace suites, guests are met with whitewashed oak flooring, floor-to-celling wood shelving, trompe l'oeil art walls by Chicago-based artist Charles Nitti, and a private terrace with a private fire pit. The larger, 1,200-square-foot Grande Penthouse has all of this and then some, including a nearly 700-square-foot parlor with 14 feet of cushy sofa, a Dalmata marble dining table, and complimentary parking for one car. In all three suites, sculpted wooden walls separate the sleeping quarters from the living area and wet bar, and the spacious bathrooms have zen spa vibes with ample natural light, rainfall showers, and Roil bath amenities.

The furnishings here are slick, largely imported, and sometimes custom-made—think couture black-and-white pendant lights from France's Designheure; coffee tables designed by Italian artist Maura Mori; and Italian-made Baxter barstools, side tables, and outdoor chairs. The Ombre d'un Glacier rugs, co-designed with Ariana Rugs, meanwhile, whispers of Jónsdóttir's native Iceland, inspired by "the black beach that sits in the shadow of the glacier." For a touch of the Bay Area, some accessories were sourced at the iconic Union Square department store Gump's.

"My vision was to create a pied-à-terre where guests are swept into a world of sensual design that begs for Champagne all day," says Jónsdóttir. And yes, there will be complimentary Champagne upon arrival. We can drink to that.

// Hotel G, 386 Geary St. (TenderNob), reservations (starting at $1,895 for the Grande Penthouse suite and $695 for G Terrace suites) are available at hotelgsanfrancisco.com