The Sazaedo Hall is actually a wooden Buddhist temple built in 1796. In shape it resembles the spiral-shaped shell of a marine snail called a sazae in Japanese hence its name.
Inside the structure there are 33 images of the Buddhist Goddess of Mercy, Kannon.
A unique feature of the building are the spiral staircases built in such a way that you never have to retrace your steps as you go up and down them.
It was designated a National Cultural Treasure in June 1996.
http://www.city.aizuwakamatsu.fukushima.jp/e/kanko/w_a/w_a070.htm