Farmacia del Cambio is a 19th-century pharmacy turned into a lovely cafe serving the most exquisite coffee, pastries, and desserts. Be there as soon as it opens or visit in the afternoon (and try to avoid weekends) because there's usually a long line, I personally think it's worth the hype amd the waiting. I also loved sitting both outside and inside (two different atmospheres - both enjoyable), but even if you get seated outside, I recommend having a look at the charming interiors.