Met at Suvarnabhumi and driven in, which takes an hour or more depending on the traffic. Your Thailand Digital Arrival Card should already be filed — it is free, mandatory, and submitted online within the seventy-two hours before you land. The evening is free. The Chao Phraya express boat runs until well after dark and costs a few baht, and it is the best introduction to the city’s geography.

An early start for the Grand Palace and Wat Phra Kaew, where the Emerald Buddha carried off from Vientiane in 1779 now sits. Wat Pho next, with the reclining Buddha at forty-six metres and the massage school that has taught in the compound since the eighteenth century. In the afternoon a cross-river ferry to Wat Arun, best climbed late when the porcelain on the prang catches the light. Dinner together.

North to Ayutthaya, the Siamese capital from 1351 until the Burmese destroyed it in 1767, when it was among the largest cities in the world. Wat Mahathat holds the sandstone Buddha head grown into the roots of a fig; Wat Chaiwatthanaram stands in Khmer style on the riverbank. We return part of the way by boat, then board the through sleeper at Krung Thep Aphiwat, which leaves late in the evening.

The train reaches Nong Khai after breakfast, crosses the Friendship Bridge and terminates at Khamsavath station on the Lao side, mid-morning. Khamsavath is one of the nine ports where the Lao eVisa is accepted, and visas on arrival are issued here as well. We check in, then take the afternoon slowly: Patuxai, and the riverfront when the food stalls open. Evening free.

Pha That Luang first, the gilded stupa that stands on the national seal, then Haw Phra Kaew, built in 1565 to house the Emerald Buddha and now a museum of Lao religious sculpture. The COPE visitor centre follows, a clear and unsentimental account of unexploded ordnance and the prosthetics work it requires. In the afternoon, Buddha Park, twenty-five kilometres downriver, built by a mystic in 1958. Dinner together.

A short railway run north — around an hour to Vang Vieng, where the line emerges from the tunnels into a bowl of limestone towers above the Nam Song. The town spent two decades with a bad reputation and has largely grown out of it. We visit the Tham Chang cave and the spring at Blue Lagoon, and there is time to kayak a quiet stretch of the river if the group wants it.

A slow morning — the viewpoint at Pha Ngern is worth the climb if you are up for an hour of steps — then the train again, an hour or so north through the mountains to Luang Prabang. The peninsula between the Mekong and the Nam Khan is small enough to walk end to end in twenty minutes. We climb Phousi hill for the sunset over both rivers, then leave the evening free.

The alms round passes before six; if you watch it, stay across the street and do not photograph the monks close up. Afterwards the Royal Palace Museum, Wat Xieng Thong with its roof sweeping almost to the ground, and the Traditional Arts and Ethnology Centre, which is the best small museum in the country. The afternoon is yours in the old town. Dinner together.

A longboat upriver to the Pak Ou caves, two hours against the current, where several thousand discarded Buddha images have been left in the rock over four centuries. We stop at a riverside village on the way back. In the afternoon, the Kuang Si falls south of town, where the water drops through a staircase of limestone pools you can swim in. Farewell dinner.

A transfer to Luang Prabang airport, which is close to the centre, for onward flights to Bangkok, Hanoi, Chiang Mai or Siem Reap. If you are heading back into Thailand overland, the same railway and the sleeper will take you the whole way. We can add the slow boat down from Huay Xai at the start, or Nong Khiaw at the end, if you have the days.