Udon Thani to Bangkok

Choose the airport before the flight. If you're catching an international flight home, fly Thai Airways or Thai Vietjet to Suvarnabhumi, where the long-haul flights leave, and skip the 60 to 90 minute transfer across Bangkok from Don Mueang. If you're heading into the city, Don Mueang has more flights on Thai AirAsia, Nok Air and Thai Lion Air and usually the lower fares.

On 12Go's board for a mid-November date, flights to Don Mueang left Udon Thani at about 07:45, 12:10, 12:45, 14:20, 18:00, 18:40, 19:20 and 20:45 for about ฿1,000–1,950, and flights to Suvarnabhumi at about 08:40, 13:55, 15:10, 17:10 and 19:40 for about ฿1,430–2,600. The airport is about 5 km south of the center, 10 minutes by taxi or Grab.

The train I'd take is Special Express No. 26 at 20:20, the sleeper with first and second-class air-conditioned berths and a restaurant car. It's a better fit in this direction than going north, because you get dinner in Udon, a full night in a berth, and Bangkok at 05:30, early enough for a morning flight from Don Mueang, where it stops at 05:13. A second-class berth costs ฿877 upper or ฿977 lower at SRT's price, and first class ฿1,313–1,513.

Express No. 76 is the day train, leaving at about 08:30 and reaching Krung Thep Aphiwat at 16:35, with seats only, ฿244 in third class or ฿477 in second. Rapid No. 134 at about 21:00 is the cheap night train, ฿204 in third class, arriving at 07:30. All three stop at Don Mueang station across from the airport, and none goes through Korat. Book on SRT's D-Ticket site, at the station, or on 12Go, which adds a fee. By SRT's booking rules, seats should open about 90 days ahead, and No. 26 fills first.

Most buses back to Bangkok leave in the evening. On 12Go, VIP buses leave between about 17:30 and 20:10, Nakhonchai Air's First Class coaches at 08:30, 21:00 and 21:45 and its Gold Class through the day and evening, and Transport Co. and other express buses at 09:00 and from 19:00, for about ฿600–840. The trip takes 8 to 10 hours, so an evening bus gets to Mo Chit 2 around dawn. Check which Udon terminal yours leaves from, because companies use Bus Terminal 1 in town, Bus Terminal 2 on the ring road or, for Nakhonchai Air, their own station.

From Nong Khai, the same three trains start 40 to 45 minutes before Udon, No. 76 at 07:45, No. 26 at 19:40 and No. 134 at 20:15. Buses from Nong Khai to Bangkok cost about ฿650–850 on 12Go, or fly from Udon Thani, about 55 km away, where a shared van from Nong Khai to the airport costs about ฿200.

From Vientiane, Rapid No. 134 leaves Khamsavath station at 18:25. Seat61 says to be there 45 to 60 minutes early for Lao exit formalities, and at Nong Khai everyone gets off with their bags for Thai immigration before the train goes on to Bangkok at 20:15. The BKS and Lao buses from Vientiane to Udon Thani leave at 08:00, 10:00, 12:00, 14:00 and 17:00, two to three hours with the border, so a morning bus still makes an evening flight to Bangkok. Our Vientiane to Bangkok guide has the No. 134 sleeper, the border and the buses.