Fukuoka > Kitakyushu >? > Beppu

Budgeting a 4 days trip in Kyushu before flying out to Osaka/Kyoto for 10 more days in early June. We have already been to Nagasaki, Kumamoto, Aso areas last year, so for this year, we want to do Fukuoka area > Kitakyushu > and on the way to Beppu before flying out of Oita.

Question is, between Kitakyushu and Beppu, is there other good stops that are "along the way" between these 2 spots? Ideally some sightseeing or another hotspring? Or if there's nothing then we can just go directly from Kita to Beppu. Thanks for your advice!

There is always something...the question is if there is something else you'd find better elsewhere in the country for your time. But a few good places are Usa Shrine - it is one of the better shrines on the island.
https://youtu.be/zzp4mbuSjz4

Another good place is the Kunisaki Peninsula. But for that, you'd pretty much need to rent a car to tour the area.
https://www.japan-guide.com/e/e4720.html

Go the other route

Fukuoka to Hita/Amagase Onsen to Yufuin to Beppu

In Kitakyushu, don�ft miss the Toto Museum

NAKATSU
I Love nakatsu city
So between kitakyushu and beppu, you can visit nakatsu or kitsuki city

Kyushu is one of my favourite locations in Japan. Do note that there is not a heap to do between Fukuoka and Beppu if you don't have a car. There is however heaps to do close to Beppu. I'll link some ideas below:

Kitsuki Castle Town: https://www.japan-guide.com/community/mfedley/report-2886

I really like this location - and it should be easily reachable via train (if there is one!) or bus.

Usuki: https://www.japan-guide.com/community/mfedley/report-2893

Usuki does not have heaps to do - but it's attractions are pretty cool and the buddhas outside are quite unique for Japan

Beppu: https://www.japan-guide.com/community/mfedley/report-2889

The hells are tacky but that's half of the fun

Yufuin: https://www.japan-guide.com/community/mfedley/report-2890

I did not like this location - others do.

Hita: https://www.japan-guide.com/community/mfedley/report-2892

If you have a car - then Hita is quite nice.

For Kitakyushu - it's an ok town but I did not find it to be a highlight. The Toto museum is meant to be good though.

I did this tour before: https://www.oitakotsu.co.jp/1day/ around the Kunisaki peninsula to sightsee some things at a very nice price..
Its a 1 day bus tour. Its in Japanese but dont let that hold you back.

Takachiho is also nice.. but little further down south and maybe out of the way. You can spend the night and see Kagura there...

Yufuin is also quite a nice place for a couple of hours.