From the outside, San Lorenzo looks like an ordinary palace wall on Piazza Castello — Guarino Guarini was told by the Savoys not to compete with the Royal Palace next door. Step inside and you are suddenly under one of the most extraordinary domes in Italy: an interlocking lattice of stone ribs that hovers above the octagonal nave like a piece of mathematics made solid.
Built between 1668 and 1687, it is one of two Guarini domes in the centre of Turin (the Chapel of the Holy Shroud, in the cathedral, is the other). Free to enter and easy to miss. Look up immediately when you walk in.