Vicus Caprarius — City of Water

An underground archaeological site beneath the streets of the Trevi district, just steps from the Trevi Fountain but missed by almost everyone throwing coins above. Descend a narrow staircase to find the ancient cistern of the Aqua Virgo aqueduct — the same water supply that feeds the fountain today — along with remains of a Roman residential block from Nero's urban planning. The space is small and atmospheric, with water still flowing through ancient channels. A thoughtful museum display explains the engineering. Weekend visits require booking ahead as the limited underground space fills quickly.