The big draw in Usuki is a series of stone Buddhas carved from soft volcanic rock about 1,000 years ago, designated as national treasures. The town itself is also worth a look, with some temples and an old district with shops and restaurants.
There are a couple of trains an hour to Usuki from Oita, a limited express which takes about 30 minutes and costs 1,670 yen and a local train which takes 45-55 minutes and costs 740 yen (both covered by the Rail Pass). There’s a little tourist information office at Usuki station (to the left at the front of the building) where you can pick up maps and bus timetables, because yet again the buses are infrequent.
There are only four buses on a weekday from Usuki station to the Stone Buddhas (Usuki Sekibutsu): 10.10am, 12.10pm, 2pm and 3.15pm. The bus costs 310 yen each way and takes about 20 minutes, but it drops you off right in the car park. If you’re willing to walk 10 minutes to bus stop Jyohoku there are more buses – and on the way back you may find yourself dropped off at Jyohoku anyway as only half the 11 buses from the Sekibutsu back into town go to the station.
When you arrive, work out when the buses leave. You’ll need at least an hour to see the Buddhas but the way the timetable falls you could end up with an hour to kill after that – in which case, a combined ticket for the Buddhas and the small historical museum next door is good value at 710 yen (entrance to the Buddhas alone is 530 yen). It’s a beautiful area in a small valley, with several temples scattered around the fields, and I heartily recommend a visit.
On the way back into town, if you get off at Hirasozu bus stop you can explore Ryugen-ji and its three-storey pagoda and walk back through the old samurai district. The maps given out at the tourist office list various different bus stops if you don’t fancy walking all the way back to the station, and you can roughly work out the times from the timetable they give you.