Khon Kaen is located about 450km from Bangkok, mid-way between Udorn Thani and Nakhorn Ratchasima. The town itself is not particularly interesting, but some of the surrounding countryside is quite scenic.
Air-conditioned buses leave Bangkok's Northern Bus Terminal at regular intervals throughout the day for the 6 hour journey to Khon Kaen. There are also regular bus services from Phitsanuloke and Nakhorn Ratchasima (Khorat).
Trains depart from Hua Lampong Station in Bangkok several times per day, and take about 8 hours to reach Khon Kaen.
Thai International have flights from Bangkok to Khon Kaen. You can get great deals on flights to Thailand here: www.cheapflights.co.uk/Thailand/
Songthaews are the best means of getting around the town. Your hotel may be able to arrange a car and driver for longer trips.