Museo della Forma Urbis

This little-known museum houses surviving pieces of the Forma Urbis Romae, a vast marble plan of ancient Rome carved in the early 3rd century AD that once covered an entire wall and mapped the city's every structure in astonishing detail. Most visitors discover it by chance or through a guide rather than by seeking it out directly, and reviewers describe genuine surprise at encountering an artifact of this historical significance in such a low-key setting.

Its low must-see score paired with a notably high hidden-gem rating captures that dynamic precisely - a niche but remarkable find for those who make the walk, though others report finding little more than a single sparsely furnished room for the ticket price. A 4.4 rating suggests satisfaction depends heavily on prior awareness of what the plan actually represents.