The Ubon Ratchathani Bus Terminal
Ubon Ratchathani is rather well connected to the rest of Thailand, and especially Bangkok. It's the 'end of the line' for one branch of the northeastern rail lines, as well as about as far east as you can go by bus.
Plane: You can reach Ubon by plane from Bangkok via the national carrier Thai Airways, and budget carriers Air Asia and Nok Air. All of the carriers generally have two flights a day to and from Ubon's airport, which is just on the edge of downtown. Air Asia also flies direct between Ubon and Chiang Mai.
Train: There are six or more trains a day between Bangkok and Ubon Ratchathani. The trip takes between 8 and 12 hours, depending on the train service selected.
Bus: There are several companies offering bus service to Ubon from Bangkok, most with up to a dozen departures daily. Most buses from Bangkok leave from the main northern bus station at Mor Chit. The travel time from Bangkok is about eight hours for the first class express buses. Note that the bus terminal in Ubon is on the far north side of town. It's actually much further away from the center than the airport. Expect to pay 150 Baht or more for a taxi or tuk-tuk from the terminal to any hotel in the center of town.