芥屋大門観光社（乗船券売場）

25 minute boat ride that stops inside cave. I think it's worth the money, just be there little earlier so you get spot and don't have to wait another 30 minutes.

Nice place, but we were unlucky and didn't go inside the cave cause of the big waves. Boat stopped in front of the cave so we can make photos, but there's were around 15 people on the boat and we didn't have enough space. Costs 1000¥ for a 20 mins boat ride. Not sure I would recommend this place to friends. Better go to a park with seven caves near Karatsu.

From here you buy your boat ticket to Keya no Oto. You can buy your ticket 5-10 minutes before the ride. It was ¥700 for a 25 minutes boat ride. The rock formation is really beautiful, if the weather and waves permit the boat will enter the hole. In my case due to strong waves we went very close in front of the hole but not inside as it would be too dangerous. On the way back they will take you to see a big round rock by Keya beach. You will be wearing a life vest the whole time on the boat and you'll be hearing recorded sightseeing information in Japanese through a speaker (with a bit of music).

Great place to go for a boat cruise.

The place with one of the most awesome sceneries