Twelve days from Bangkok to Ho Chi Minh City: the run that made Southeast Asia a circuit

A plain looking temple at the eastern end of Chinatown holding five and a half tonnes of solid gold in the shape of a seated Buddha. It spent centuries under a coat of plaster, disguised from Burmese invaders and then forgotten, and the covering only cracked open in 1955 when the statue was being moved to a new building.

The biggest and busiest Chinese temple in Bangkok, founded in 1871, with a century and a half of incense soaked into the timber. Walk in through the dragon gate off Charoen Krung, take the offering hall slowly, and come out into the flower and medicine shops on Soi Itsaranuphap.

The street food stalls set up around six and run past midnight: grilled river prawns, oyster omelettes, guay jub noodles in peppery broth. Pick a stall with a queue of locals and point. Cash only, and the good places sell out.

Rama I began building it in 1782 when he moved the capital across the river, and it stayed the royal residence for a century and a half. The royal chapel inside the walls holds the Emerald Buddha, a jade figure less than seventy centimetres high whose robes the king changes three times a year. Go straight there first, then work back through the throne halls.

Ten minutes south of the palace gate and the better temple of the two. The reclining Buddha is forty six metres long with mother of pearl inlay on the soles of its feet, and the surrounding compound is the country's first public university, its walls carved with the medical and astrological knowledge of the day. The massage school still operates on site.

The lanes between Wat Pho and the pier do noodle soup and rice plates for next to nothing, and there are a couple of air conditioned cafes in restored shophouses on Maha Rat Road if you need an hour off the heat.

The crossing costs a few baht from Tha Tien and takes four minutes. The central prang stands about seventy metres and is faced entirely in broken Chinese porcelain, ballast from trading ships pressed into the plaster. Climb the steep steps if the heat allows, and note that the best view of it is from the bank you just left, at dusk.

Six traditional teak houses, bought in pieces around the country and reassembled beside a canal in 1959 by an American architect who had served in the OSS during the war and then rebuilt the Thai silk trade almost single handed. He walked into the jungle in the Cameron Highlands in 1967 and was never found. Entry is by guided tour only and they run every twenty minutes.

A four faced golden Brahma on a traffic island at the Ratchaprasong junction, built in 1956 after a run of accidents during the construction of a hotel behind it. It is the busiest working shrine in the country: dancers in traditional costume are paid by petitioners to perform, and the marigolds and incense never stop. Five minutes on foot from the Skytrain.

Not a compromise. The food courts under the Siam malls are where office Bangkok eats: buy a stored value card at the counter, walk the stalls, and get better som tam and boat noodles than most restaurants manage.

The highest observation deck in Thailand, on a tower whose facade looks like a column of pixels falling out of place. The rooftop at 314 metres has a glass tray you can stand on and no railing between you and Silom. Time it for forty minutes before sunset and stay for the lights coming on along the river.

Around an hour from Suvarnabhumi. Agree a taxi fare at the desk in arrivals or book the hotel transfer; the ride in from the new airport is about forty five minutes on a good new road.

Eight galleries laid out chronologically, with a room of a thousand Buddha images and, more usefully, a clear account of who built what and why. Half of Angkor is Hindu and half Buddhist and the switch happened more than once. An hour and a half here saves you a great deal of confusion tomorrow.

A working temple in the middle of town with a five hundred year history under some very shiny recent gilding. Monks study here, the reclining Buddha pavilion is open to anybody, and at dusk the whole compound fills with families. Ten minutes on foot from the river.

Pub Street itself is a lot. One block either side, the lanes around the Old Market do amok trey, fish steamed in banana leaf with coconut and lemongrass, and Kampot pepper crab, for half the price and a tenth of the volume.

Built for Suryavarman II in the first half of the twelfth century as a Hindu temple to Vishnu, and turned Buddhist a few generations later without ever being abandoned, which is why it survived. It faces west, unusually, which is also why sunrise puts the towers against the sky rather than into it. Climb to the upper level early: numbers are capped and the queue builds fast.

Jayavarman VII's state temple at the centre of Angkor Thom, its towers carved with enormous serene faces looking out in four directions. Nobody agrees whether they are the Buddha or the king. The lower gallery reliefs are the other reason to come: market scenes, a cockfight, a woman giving birth, and a naval battle against the Cham.

The stalls opposite the Terrace of the Elephants do fried rice, noodles and cold drinks, and your driver will steer you to one where he eats free. That is the arrangement and it is fine. Sit out the worst of the afternoon heat here.

The temple left in the grip of the forest, where silk cotton and strangler fig roots pour over the galleries. It was a Buddhist monastery founded in 1186 and once housed several thousand people. Go late in the afternoon when the tour buses have gone; the light through the trees is better and the famous doorways are briefly free.

Consecrated in 967 and built not by a king but by a courtier, which may explain the scale: it is tiny, and every surface of its pink sandstone is cut with a depth the larger temples never attempt. Deities, guardian monkeys, whole scenes from the Ramayana in relief a few centimetres deep. It opens at half past seven; be there for it and you will have the place nearly to yourself.

Jayavarman VII built it in 1191 on the site of a battle won against the Cham, and lived here while Angkor Thom was under construction. It is enormous, largely unrestored, and half swallowed: collapsed lintels, a two storey building with round columns that belongs nowhere else in Angkor, and a corridor running most of a kilometre east to west. Walk it end to end and come out the far side.

The riverside cafes near the Old Market do good Khmer curries and better iced coffee, thick with condensed milk. Then take the afternoon off; you have earned it and the heat is at its worst.

A circus with no animals, run as a school for children from difficult backgrounds, telling Cambodian stories through acrobatics and live music. It is genuinely good rather than worthy, the tent seats a few hundred, and the shows sell out in high season. Book in the afternoon for the evening performance.

Six hours on National Road 6 with Giant Ibis or Mekong Express, both of which leave from central Siem Reap between seven and eight and drop in central Phnom Penh. Book the day before, take a jumper for the air conditioning, and sit forward of the wheels.

Built from 1866 when the capital moved back to Phnom Penh, and still the king's residence, which is why part of it stays shut. What is open is the throne hall and the Silver Pagoda, rebuilt in 1962 and floored with more than five thousand solid silver tiles, most of them kept under carpet to protect them. Shoulders and knees covered, and last entry is well before closing.

The riverfront promenade runs a couple of kilometres along the Tonle Sap to where it meets the Mekong, and the whole city walks it at dusk: aerobics classes, kite sellers, monks, and a line of bars in French colonial shophouses on the landward side. Walk north until you find one you like.

Cambodian food is milder than Thai and sweeter than Vietnamese: try lok lak, seared beef with a black pepper and lime dip, and anything cooked with Kampot pepper, which is the country's one world class ingredient.

A suburban secondary school that the Khmer Rouge turned into Security Prison 21 in 1975. Estimates of the number held here run between twelve and twenty thousand, and the survivors are counted in single figures. The classrooms are left as they were found, with the iron beds still in them and the regime's own meticulous photographs of every prisoner on the walls upstairs.

Fifteen kilometres south of the city, the orchard where prisoners from S-21 were taken to be killed. It is quiet now, grass and a lake and a few wooden shelters over the excavated pits, with a memorial stupa in the middle holding thousands of skulls arranged by age and injury. The audio guide again, and allow the full circuit.

The cafes around the Independence Monument and along Street 240 are the easiest reintroduction to the ordinary world: good coffee, air conditioning, and nobody expecting you to talk.

A terracotta red pavilion with a courtyard garden, opened in 1920, holding the best collection of Khmer sculpture anywhere. The eighth century pieces from before Angkor are the surprise, and the reclining bronze Vishnu recovered from the West Mebon is the single finest object in the country. An hour and a half is plenty.

Six to seven hours including the border, leaving Phnom Penh from about six in the morning. Have the Vietnamese e-visa printed, keep the passport and paperwork on you rather than in the hold, and expect a small dollar fee at the Cambodian side.

The boulevard between the city hall and the river was pedestrianised in 2015 and it is where Saigon comes out in the evening: skateboarders, wedding photographs, families, and a fountain the children stand in. At Tet it is planted end to end with flowers.

Built as the Hotel de Ville between 1902 and 1908, cream and yellow with a clock tower, and now the seat of the city government, so you admire it from the outside. It is floodlit from dusk and it anchors the far end of the walking street.

Banh mi from a pavement cart, com tam with grilled pork over broken rice, or bun thit nuong. Saigon eats standing up and on plastic stools, and the best food on this entire route is sold within two hundred metres of wherever you are sitting.

The presidential palace of South Vietnam, rebuilt in the 1960s by a Vietnamese architect trained in Paris and left exactly as it was found: rosewood cabinet room, a helicopter on the roof with two bomb craters marked beside it, and a command bunker in the basement with the radio equipment and wall maps still in place. The building alone is the best sixties architecture in the country.

Opened within months of the end of the war and renamed in 1995, it is unsparing and crowded and quiet. Captured American aircraft and armour in the yard, a reconstruction of the tiger cages from Con Dao, and rooms on the effects of dioxin that many people cannot finish. Go early in the day rather than late.

The streets north east of the museum are full of com binh dan places, the rice shops where office workers eat: point at four dishes behind the glass and pay about two dollars. Iced tea comes free.

The twin brick towers at the top of the walking street were built between 1877 and 1880 with materials shipped from Marseille, and the brick has never been rendered or painted. It has been under restoration for years with scaffolding on the facade and the interior shut to visitors, so treat it as something you look at rather than go into, and check locally before making the walk.

A temple founded by Cantonese immigrants for Mazu, the sea goddess who protected them on the crossing, and rebuilt more than once since the eighteenth century. The roof ridges carry whole ceramic villages of figures, and enormous incense coils hang from the ceiling of the main hall, burning for weeks with prayer slips tied to them. Take your shoes seriously and your camera quietly.

The wholesale market at the heart of Cholon, built in 1928 by a Chinese businessman and reopened in 2018 after a long restoration. It is arranged around a clock tower and a courtyard garden, and it sells to shopkeepers rather than tourists, which is exactly what makes it worth an hour. The food stalls on the perimeter open at dawn.

This is the home of hu tieu Nam Vang, the Phnom Penh noodle soup that travelled the other way down the road you have just driven, served dry with the broth on the side. Any shop with a steel cart out front will do it well.

Two hundred and sixty two metres on the riverbank, with a helipad stuck out of one side like a diving board, and a viewing floor on the forty ninth. It is lower and cheaper than the newer tower across the water and the view is better for it: you are close enough to watch the traffic knot and unknot at the roundabouts below.

The market hall with the clock tower has sold to tourists for decades and the stalls know it, but the food section along the northern side is the real thing and it opens at six. Pho, bun bo Hue, banh cuon, and coffee thick enough to stand a spoon in.

Ca phe sua da, dripped through a metal filter over condensed milk and poured onto ice, is Vietnam's great contribution to the morning. Order it at a pavement stall and sit on the low stool facing the street, which is how it is meant to be drunk.