The height of summer seems perhaps a foolish moment to begin thinking about one’s life indoors again but why ever not? There’s no time like the present to ponder spaces that blend exterior and interior for maximum enjoyment.

One of the finest such rooms was created by and for Elsie de Wolfe (1858–1950), a mediocre but marvelously dressed American stage actress who transformed herself into a great international decorator known for popularizing flowered chintz, mirrored surfaces, 18th-century French furniture, and textiles that mimicked zebra and ocelot hides. She also was an early and enduringly enthusiastic proponent of plastic surgery, but that’s another story.

At Villa Trianon, De Wolfe’s country house on the edge of the royal park at Versailles, she conceived a terrific glazed chamber that was part sunroom, part salon, and all relaxed glamour. Enclosed with sheets of glass—previously it was an open veranda—and overlooking an emerald lawn dotted with amusing topiary, the space looks as invitingly modern here as it did in the 1930s, back when waltz-weary guests poured onto the porch from the adjacent gallery. (This photograph was snapped in the early ’80s, shortly before Villa Trianon’s influential contents were auctioned off.) It’s a refreshing room, too. Mirror panels the rear wall, reflecting the garden as well as the scalloped awning roof and giving the square footage the breezy feeling of a transparent pavilion embowered by greenery.

Rather than deploy a suite of matching furniture (frequently the death knell of style, as far as I’m concerned), De Wolfe gave her getaway the cozy aura of a living room, blending shapes, styles, and materials into an inviting whole.

Smart wicker armchairs with fat cushions and a couple of metal side chairs with sling seats stand on the wall-to-wall matting, joined by an iron daybed, a small sofa, and a capacious banquette, the last two tautly dressed in orange Venetian sailcloth—a trend of the early and mid-20th century that really should come back into favor. A bit of bamboo here, a neoclassical console there, and lots of cushions for sinking into for hours with a cool drink at one’s side and an absorbing book in one’s hand—et voilá, a porch for all seasons.

Make that nearly for all seasons. Ensuring that the space was fully functional year-round would be my only alteration. (De Wolfe tended to summer at Villa Trianon and spend the cooler months in her elegant Paris penthouse.) I’d install a fireplace or one of the tall European ceramic heating stoves that De Wolfe so greatly loved and hoped, in vain, that Americans would learn to embrace.