Barcelona
A beach, a mountain and Gaudí, all reachable on foot from a single apartment.
Three thousand years of layers, and the best carbonara within a mile of anywhere.
Rome is the most concentrated historical city in Europe — you trip over ruins on the way to dinner. The famous sights deserve their reputation, but the version of Rome people fall in love with is usually the quieter one: an early morning in Trastevere, an aperitivo in a piazza, a plate of cacio e pepe done properly.
It's also crowded, hot in summer, and unforgiving if you don't book. Two or three pre-booked anchors per day and a lot of unstructured walking is the formula that works.
Warm, long evenings, and the queues are half what they are in July.
A workable shape rather than a schedule to obey — two fixed things a day, and room to change your mind.
Almost entirely on foot; the centre is smaller than it looks. Metro line A and B cover the long hops, buses are slow, and taxis are best pre-booked by app. Cobbles punish bad shoes.
Rome's constraint is restaurant capacity — trattorias are small and won't seat six without notice. Assign one person to book dinners before you fly and keep the reservations somewhere everyone can check.