One of the few visible remains of Roman Lutetia, the Arènes de Lutèce is a first- or second-century amphitheatre that once seated some 15,000 for gladiatorial combats and stage shows. Lost for centuries and rediscovered during nineteenth-century roadworks, it now sits hidden behind a ring of apartment buildings off the Rue Monge, reached through an easily missed passage.
Today it is a free public garden where locals play boules and football on the old arena floor and teenagers lounge on the surviving stone tiers — history put to thoroughly everyday use. It takes ten minutes to see and makes a quiet, atmospheric detour between Rue Mouffetard and the Jardin des Plantes.