Buses make useful connections around Kyushu, and if you don't have a JR Rail Pass, they are often much cheaper than the trains. For example, the bus between Nagasaki and Kumamoto is half the price and takes about the same time; plus you don't have to make any changes or wait for connections, as you do with trains. A highway bus makes a trip between Kumamoto to Yufuin, either direct or with a stopover at the Aso-san crater. The Kyushu Express Bus Portal Site is a great way to check on bus times and prices.
Kyushu Express Bus. 0120/489–939; www.atbus-de.com.e.jo.hp.transer.com.