I visited Teshima back in October this year, primarily to visit this space - it is so beautiful, but the one thing that isn't apparent from the photos is the acoustics! Being inside there was one of the most exquisitely beautiful acoustic spaces I have ever been in. Due to the floor and ceiling being almost porcelain like in smoothness, and the fact that the height from floor to ceiling varies so much, the space is full of the most complex delays I've ever heard - the dozen or so people in there when i visited were all being very quiet, but even the smallest sounds literally shimmer!
I love the Seto Inland Sea - a visit to Teshima, Naoshima & Shodoshima is totally worth it!!!
FWIW I posted some photos of it & two other acoustic experiences I had in Japan recently... http://www.musicofsound.co.nz/blog/acoustic-epiphanies-in-japan