Chong Mek is a township in Isaan.
A taxi can be rented from the taxi counter at the Ubon Ratchathani airport or bus terminal at roughly 1000 Baht. The trip takes under an hour at a distance of 60 km. Buses (called rot tour or rot air by Thais) also make their way to Chong Mek from the bus terminal. Depending on the bus you may need to switch buses at Phibun Mangsahan.
Chong Mek was once a thriving market selling cross-border goods popular with Thai tourists. Most of the bustle has moved to the market in Mukdahan since the opening of the Friendship Bridge 2 in 2006.
Take a bus to Ubon Ratchathani (1.25 hours, 60 kms) or cross the border into southern Lao and take a bus to Pakse (45 mins, 45 km)