"The Sir John Soane's Museum has opened an exhibition focusing on the classical orders of architecture. It draws on the enormous collection of around 30,000 drawings and watercolours that grew out of Soane's fascination for learning the language of architecture and reinterpreting it in original ways."
This from the edition of RA that only arrived this morning, so it's a bit out of date - the exhibition has been open since 16th October and will last until the end of January. Free admission. http://www.soane.org/next.html