Rome is riddled with catacombs and underground tunnels, but few are as intriguing as the catacombs of San Callisto.
These early Christian tombs are a variety of different shapes and sizes, and once housed the remains of up to half a million people.
Although they're on the outskirts of the city they still don't manage to escape the tourist scrum, but with nearly 20km of tunnels it's undeniably worth it.
Via Appia Antica 110-126
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