When I was a kid, when you went to Mallory Square to watch the sun set, it set behind a scraggly island full of huling fuel tanks. It was part of the charm. When the sun vanished behind the dilapidated rusty metal, the day was done.

How things change. The onetime Tank Island was cleaned up in the 1980s, renamed Sunset Key—you won't find many staffers willing to cop to the island's shady past identity—and now it's the ne plus ultra of Key West's exclusive romantic getaways. Guests arrive and check in at the Westin on land, and then, flashing their gold key card they are ferried from the dock beside Mallory Square to the far side of the island, where they enter a gardened idyll of porches and Adirondack chairs, respectfully spaced and spacious cottages furnished like private homes, a private swimming pool with bar, and a west-facing restaurant, Latitudes. None of it feels very specific to Key West—even the soft sand on the designated west-facing beach was brought in from the Bahamas, since the local beaches are rocky. But when your days are this indulgent, who cares? Continental breakfast is delivered in a basket each morning, niceties such as Wi-Fi are free to use, and although the hubbub of Old Town is just 10 minutes away by boat (they go twice an hour and by demand in the middle of the night), you'd never know it among the flowers and lawns of Sunset Key.

Although it's priced like one, it's not a fully five-star experience (the staff knows when to keep its distance) and although it's impossibly romantic, not everyone who stays at Sunset Key is celebrating a wedding or a Golden Anniversary. It attracts its share of families, and beyond the standard one- and two-bedroom cottage types, there are three multi-bedroom houses with full kitchens, private pools, and westerly views. The southern half of the 27-acre island, forbidden to guests, is full of private homes that are cut from that same mold—locals still gossip about the year when Oprah flew all her friends to Key West and took over the ultra-private Sunset Key to celebrate her own birthday. "But why would she want to party on Tank Island?" the old Conchs said. Clearly, they've never been invited over.