Fukuoka to Karatsu

Hello all,
Would like to have some input for a day trip from Fukuoka to Karatsu:
a. What is the convenient way for travel from Fukuoka to Karatsu, is it by train or bus?
b. Any recommended day pass for the travel?
c. What is the most recommended attractions?

Thanks & Best Regards,
WL

You can visit unlimited time between Fukuo ka to karatsu by JR Fukuoka wide rail pass 2 Day =3060 Yen

c. What is the most recommended attractions?
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Please refer to here.
https://www.japan-guide.com/e/e8375.html
https://www.karatsu-kankou.jp/en/

We went by train, the journey is very pretty in parts and follows the coastline. I would say it is one of the nicer train trips I've had in Japan

I'd take the train - and if doing a bit more than just that round trip, then using the Fukuoka Wide Pass as mentioned above. There is not that much that is extremely impressive - but the castle has some charm, and if the weather is good, then the view from atop Mt Kagamiyama is spectacular. I rode my motorcycle up there (and the 26+ hairpin turns multiple times) and it is well worth it. If you are willing to rent a car, then a whole lot more places become available. There are a few hidden gems to explore, like Mikaeri Falls which is especially nice after it rains, plus if going in the warmer months, there are several excellent places for the terraced rice fields (tanada, or dandan batake) like Hamanoura, Oura, Urigasaka, and others.

If you do opt for the Fukuoka Wide Pass, please be aware it does not cover the Fukuoka subway.

There used to be subway train bound for Karatsu/Nishi Karatsu once or twice in an hour but not any more. Typical transfer is in Chikuzen Maebaru station instead of Meinohama. Self drive is more preferable to extend explore regions in Karatsu.