Named for its most famous barfly, the ubiquitous Count Cavour, this beautiful historical room combines a magical, mirrored setting with a great collection of contemporary art and design savvy. Upstairs from Del Cambio, a Michelin-starred restaurant, the aperitivo here doesn't come cheap (around €15) but features artfully prepared cocktails served with quality snacks (including a mini tin of polenta). Reserve ahead.
There's a bar menu until midnight (it can be hard to tear yourself away once in its luxurious thrall) and a velvet clad smoking den.