I'm wondering if it might be Japanese Red Pine. Not like the stuff we're used to in the west. Very resistant to rot, used traditionally for bridge piles, with an oily texture. Having said that, I've just looked it up. It's in Hishino, in southern Japan. Haven't come across any info on the timber species, but found out this: Originally built about 250 years ago, but famous now mainly for three aspects: 1) that it's a rare triple-wheel system; 2) that it's made without nails or other metal fastenings; and 3)...that it gets completely rebuilt every five years! So I reckon our original thoughts were along the right lines!
