I had the pleasure of going back to Beppu on business and staying at the Nishitetsu Inn right downtown.
Having just spent 3 weeks in the US, I thought, "I could really use an onsen" Then I got the call, and the job required me to spend the night.
The onsen is clean and spacious and pretty good as far as low-end business hotels go. The faint whiff of chlorine was a turn-off, but the temperature was nice.
Having lived in Fukuoka for almost 1.5 years now, nearby onsens are truly one of those things I miss.