It is Pi day, in those nations where the month comes first and it is 3.14, when we celebrate all things mathematical and round, and top it off with a bite of pie. We recall on this day Rolf Disch's solar powered house that tracks the sun, so that its triple-glazed front can face the warming sun in winter and show its well insulated back in summer. Then there is the wonderful water tower conversion by zecc arcitechten of Utrecht. A pie shaped kitchen would be an interesting place to work, and then there is Eli Attia's way too big Round House. Happy Pi day!