I was lucky enough to get to the Nanto brewery on Okinawa. Not Japan main island but you might see it there.
They use an old cave systems water to brew the beer that you can visit at "Okinawa world"
Pretty good I even brought back 2 bottles.
I've been very lucky to visit a lot of places and the Japanese culture is by far top 3 most amazing I've experienced.
You'll love it!