Palazzo Madama in Turin

You're standing on Piazza Castello, in front of Palazzo Madama. Start with that white stone façade. Giant columns, tall arched windows and a balustrade lined with marble vases and statues. It looks like a vast Baroque palace. But it's really a stage set. Behind that front there's just one room's depth of new building. Architect Filippo Juvarra started it in 1716, and by 1721 work had stopped. Only the front ever got finished.