Abukumado Caves are in Fukushima prefecture near to a town called Tamura. The limestone caves were discovered in late 1960’s and have been developed as a tourist attraction.
They stretch for a few hundred meters inside the mountain and a pathway has been created to walk through and view the lights illuminating the stalactites and stalagmites.
Its quite cool inside and a local vineyard stores wine inside the caves (locked cages unfortunately) but apparently safe from weather and earthquakes..
Just Life in Japan 