Pillow talk was a powerful weapon for gathering intelligence during the Vietnam War, with bar girls among recruits passing information to Viet Cong spymasters.
Another celebrated example of successful espionage: a simple noodle shop — frequented by United States and other military officers because of its superb pho (noodle soup) — was run by a communist commander. Waiters reported overheard conversations and their boss passed the intelligence to guerrilla leaders, who would adapt their plans accordingly.
Ho Chi Minh City — formerly known as Saigon, a name that is still commonly used — teemed with spies during the Vietnam War's two decades, culminating in communist victory in 1975.
Secret agents and their handlers met in then-decrepit hotels to deliver or receive information. Rumours about spies' identities were common topics of conversation.
But times have changed dramatically. Vietnam is at peace. Tourism has become a big industry — and faded colonial hotels are recognised as architectural gems, expensively refurbished and restored to their original glory.
In this city, colonial-era hotels are a colourful but comfortably upscale alternative to global accommodation chains. Rooms are of the same standard and similarly furnished to those at the city's other leading hotels.
Two of the oldest, the Grand (formerly the Saigon Palace) and the Majestic - both raised to five-star standard - have become so popular with foreign visitors that new wings have been built to increase room numbers. Staff say frequent visitors can tell the difference — and often prefer staying in the original sections.
Another old hotel, the Caravelle, isn't really colonial - it opened in 1959, four years after independence — but is often grouped in this category because it, too, is steeped in modern Vietnamese history.
The Caravelle, which also sports a new wing, was called the Doc Lap (Independence) from unification in 1975 until 1998, when it reverted to its original name.
The rooftop of its old wing, now called the Saigon Saigon Bar, has panoramic city views and was a sunset hang-out for war correspondents during the conflict. Back then the building also housed several embassies — including Australia's - as well as the offices of several television networks. In the lobby, spies mingled with guests while waiting to meet their paymasters.
Today the Caravelle, which is popular with Australians, bridges the gap between old and new.
Celebrity guests have included former United States President Bill Clinton, former South African President Thabo Mbeki, Britain's Princess Anne and actor Sir Michael Caine (when he was filming a remake of The Quiet American, directed by Australian Phillip Noyce). The film was partly set across the street in the Continental — another famous and refurbished colonial hotel.
It was at the Continental that Graham Greene wrote part of the novel on which the movie was based.
During the Vietnam War (called the American War in Vietnam), US secret agents often met their Vietnamese contacts at the Continental or nearby cafes. An inner courtyard was - and still is — a well-reviewed place to dine.
The Continental is a few minutes' walk from another hotel, the Rex, where the American military held daily wartime briefings that some correspondents nicknamed "the five o'clock follies".
Vietnam's most successful spy, Pham Xuan An, was a frequent visitor to the Continental. His cover: he worked for western publications, including Time magazine, as a journalist and "fixer". But An was secretly a committed communist, and his reports were avidly read in Hanoi.