According to the Wikipedia article you linked all of these sculptures are made of Gauinger Travertin, see
An dem vom Mitte September bis Mitte Oktober 2000 ausgerichteten Bildhauersymposionnahmen nahmen zehn Bildhauer teil, die alle den gleichen Naturstein bearbeiteten, den Gauinger Travertin.
I would tag this as material=stone + stone=Gauinger Travertin
wheelchair=* describes, if an object is accessible for a wheelchair user without external help, as described on the wiki page.
I am not familar whith Panoramax but it has been discussed in the forum earlier. There are also other image hosts like Imgur etc. which are linked occasionally.