Hat designer extraordinaire Philip Treacy puts another feather in his cap: the dazzling interiors of a new hotel in his native County Galway, Ireland.

Philip Treacy wants Marilyn Monroe’s eyelashes. The fake ones, of course. "She used them to great effect," says the Irish milliner, who has adorned both heads of state (Queen Elizabeth II) and head cases (Marilyn Manson). "They come up for auction every now and then."

Recently, however, after splurging on a $45,000 Irving Penn photograph of fifties "it" girl Jean Patchett at Christie’s London during an art-acquisition spree for the new G hotel in Galway, Treacy wavered, and another fan nabbed the lashes. "Did you know she came to Galway?" Smiling, he points out that during her visit to this medieval city on the west coast of Ireland no one recognized her. "She was having a day off from being Marilyn Monroe."

The morning sun lifts the sea fog obscuring Galway Bay. We’re in a taxi van on a hunt for the 37-year-old designer’s favorite landmarks, some of which influenced his first hotel project. The blinkered fashion world might speculate about why he has chosen to expand his brand via a boutique property in an Irish backwater. But exploring his home turf with him makes it evident that this was a nostalgic move by the reserved couturier, who is encamped here with his two Jack Russell puppies, on his own break from being Philip Treacy.

Born in the isolated village of Ahascragh, an hour east of Galway City, Treacy left Ireland to study fashion at the Royal College of Art in London. In 1994, he opened a small hat shop in Belgravia’s Elizabeth Street and quickly became famous for his fanciful collaborations with Karl Lagerfeld, Valentino, and Alexander McQueen. He rarely has time to spare for visits home, and he’s only in town now for business: bringing his witty, provocative aesthetic to the G, a steel-and-glass complex overlooking Lough Atalia, in partnership with the local architectural firm of Douglas Wallace and the Irish group Monogram Hotels. Treacy’s return to his formative stomping ground is timely. Galway has been gaining attention as a seaside bolt-hole for euro-flush Dubliners and as a gateway to Connemara for nostalgic Celts on the other side of the Atlantic. And whether the small city is ready or not, the G is about to pull it into the 21st century and permanently alter notions about Irish style.

Visual references at the G include Versailles, the Ziegfeld Follies, and Andy Warhol. A long public gallery punctuated by a catwalk carpet in raspberry red opens onto drawing rooms that would titillate Marie Antoinette. The silver-toned Grand Salon is Treacy’s own Hall of Mirrors: more than 300 bubble lights designed by Tom Dixon cascade from the ceiling, and Swarovski crystals stud Plexiglas cocktail tables positioned to catch the light from floor-to-ceiling windows. The Pink Salon, where Treacy has placed both the Penn portrait and an informal snapshot of Monroe that she bequeathed to her secretary, is defined by hot-pink camouflage-print sofas. "I didn’t want the G to be ‘souvenir Irish,’" Treacy explains. As we walk down Quay Street, Galway’s pedestrian artery, Treacy points to a row of vivid Georgian shops festooned with hanging baskets of fuchsia and petunias. "Maybe it’s the grim weather. We’re not afraid of color," he says of the Irish affection for a boisterous palette. "I had an aunt who used to paint her house a different shade—orange, green, wine red—every month. That’s why there’s a lot of color in the hotel. It showcases my taste.”

Treacy’s taste also embraces iconic women beyond Monroe, including his 96-year-old London neighbor, actress Luise Rainer, who starred in The Great Ziegfeld, and clients such as Angelica Huston, Madonna, and Camilla, Duchess of Cornwall. Linda Evangelista, who modeled the twisted birdcage hat that landed him his first cover for British Vogue, has lent her name to a suite at the G. Treacy frequently collaborates with other artists, and he invited some friends to enhance the hotel’s vibe. E’SPA guru Susan Harmsworth created treatments for the G’s rooftop spa. Fashion illustrator David Downton contributed sketches for the guest rooms. For the public areas, rock musician Dan Donovan curated "sound zones" ranging from moody Brian Eno ambient to Groove Armada techno dub. Yes, there’s Irish music, but in keeping with Treacy’s avoid-the-obvious credo, Donovan sampled symphonic compositions by John Reynolds, Sinéad O’Connor’s producer.

"Let’s visit the swans...They’re beautiful," Treacy urges. We head to the canal basin near Nimmo’s Pier and he plops down on a quay spattered with gull droppings. A bevy of greedy swans snatches at bread scraps. Treacy’s mother raised chickens, geese, and ducks: he has had a fascination with feathers since childhood. One of his most remarkable hats is a ship shaped from quills and pearl buttons, which he fashioned after reading about a naval battle in historian Olivier Bernier’s Pleasure and Privilege: Life in France, Naples, and America, 1770-1790. Treacy channels ideas from "whatever is in the wind," he says. His breezy sources have included a TV documentary on UFO’s in Roswell, New Mexico, and the horns of an English Soay ram owned by his bohemian patron and mentor Isabella Blow. Analyze his wildest constructions—a shiver of monarch butterflies, a lurid orchid, a nest of hungry crows—and you’ll be persuaded that Treacy is an engineer miscast as a milliner. "He thinks in 3-D," says the G’s Irish architect, Hugh Wallace, who sought Treacy as the hotel’s genius loci. "He understands space. Most designers can’t do this. But he gets it." Monogram Hotels owner Gerry Barrett sums up why he tapped Treacy to art direct his Galway flagship: "He’s the only Irish designer with international recognition." Across the Atlantic, that profile is about to be elevated further. Although Treacy’s capricious headdresses have been exhibited at the Victoria & Albert, Milan’s Fondazione Nicola Trussardi, and the Powerhouse Museum in Sydney, their first fashion-art acknowledgments in the United States will come this month, at the Costume Institute of the Metropolitan Museum of Art, and again this summer, at the Cranbrook Art Museum in Michigan.

Our taxi detours to the Galway suburb of Salthill, where we stop at Blackrock, a concrete outcropping next to the Seapoint Promenade amusement park. Dominated by a cankerous yellow diving tower, this saltwater swimming hole is crawling with kids, who take turns cannonballing into the steely Atlantic. Once a year, when he was a child, the 11 members of Treacy’s family would squash into a borrowed car and head for this "leisure land" extravaganza, with its Ferris wheel, fish-and-chips shops, and amateur street performers. Now, the lanky blond sits incognito among the damp, jolly throng and contemplates the astonishing play of cloud and light on the bay. "I associate Galway with the sea. It smells so fresh," he says.

We pause for a nip outside Tigh Neachtain, one of Galway’s oldest pubs. Treacy is perfectly in his element on this hectic street corner; he’s equally at ease on Paul Allen’s yacht in St. Bart’s, at the Esalen Institute in Big Sur, at Titian’s tomb at Santa Maria Gloriosa dei Frari in Venice, and at the Tramway Diner on Second Avenue in Manhattan (where he loves the French toast). When discussing his favorite hotels, some of which colored his notions for the G, he mentions iconoclastic hideaways such as Casa de Madrid in Spain and the obsessive-compulsive Madonna Inn at San Luis Obispo. "The G has elements of everything I’ve learned since I left Ireland," Treacy says.

While we’re inside ordering Irish coffees, an excited girl wearing a gaudy bucket hat works up the nerve to interrupt. "Are yis Philip?" she asks. He nods politely. Galwegians may have trouble recognizing Marilyn Monroe, but they can pick out one of their own.

Just before lunch, we load Treacy’s terriers, Harold and Archie, into the taxi and set out for Connemara. Northwest along Lough Corrib, toward the 4,900-acre national park, the view turns wild—a spine of black mountains, tumbled boulders, pink heather, flocks of sheep. We pull off the road to admire Killary Harbour, a narrow seaway between craggy bluffs. Treacy wanders into a mossy field, skillfully avoiding the soggy loam, following a path of lichen-crusted rocks. His spotlessly groomed puppies grab at the chance to run amok. They charge straight for a turf pit filled with tannic-looking water and, without hesitation, fling themselves in. "It’s just a bog," he laughs, hauling them out by the collar. The dogs’ white coats have turned peat green.

In Leenane, we order fried cheese and brown bread with smoked salmon at the Blackberry Café. Our oysters were harvested just outside the front door. The gray clouds that have mantled the higher elevations all afternoon are slowly descending to sea level. We’re way out in An Gaeltacht, where residents switch from English to Irish with ease. Road markers are printed in both languages, but the translation is often comically inaccurate, as we discover when the van reaches Port na Feadóige, which means Bay of Plovers. The sign reads "Dog’s Bay." That suits our canine companions. Treacy says he collects seashells, and sets off on a hunt for specimens. The light has turned a dark silver, which matches the tarnished sea lapping this sheltered cove. Treacy stands at water’s edge as little Archie bobs like a white buoy in the gentle swell, paddling furiously after a gnawed tennis ball. While playing catch on the shore, the shy Irishman finally forgets he is under scrutiny. He unzips his tight black windbreaker, loosens his royal-blue collar, and for an unguarded moment, reveals the emblem on his T-shirt underneath. It’s the Cat in the Hat.

"When Philip Met Isabella," Cranbrook Art Museum; Bloomfield Hills, Mich.; 877/462-7262; www.cranbrook.edu; June 4-August 13.

Shane Mitchell is a contributing editor for T+L.