Either intentionally or unintentionally. Include location and sculptor, if known.

The Found Math galleries at the MAA website include many mathematical sculptures. 


Among several of his sculptures, personally for me the neatest one  (it's at the Newton Institute) 


George Green's windmill in Nottingham has a sculpture with a mill wheel with Green's Theorem carved into it. 


Perhaps these are too small to count as sculptures, but there is quite a respectable collection of models of mathematical objects on display in the Mathematical Institute in Goettingen. 


The french sculptor Bernar (sic) Venet: see http://images.math.cnrs.fr/BernarVenetdelartetdes.html 




