The entrance to one of Paris's oldest monuments looks like a normal apartment building. Number 49 Rue Monge gives nothing away, but step through, and you'll find the Arènes de Lutèce, a 2,000-year-old Roman amphitheatre that once seated 15,000 spectators for gladiator fights, chariot races and theatrical performances.

The arena served Roman Lutèce, a modest city of perhaps 10,000 people. After centuries of neglect and overgrowth, it nearly vanished for good in the 1850s when developers eyed the land. Victor Hugo personally campaigned to save it, and the amphitheatre survived, now hemmed in by 19th-century apartment blocks that hide it so completely you can walk past without knowing it's there.

On sunny afternoons, locals play pétanque on the ground where Romans once wrestled. VoiceMap's self-guided audio tours trace the full arc of Roman Paris here, connecting the Arènes to the Cluny baths, the old aqueduct and Marie Curie's Latin Quarter.