Beneath Odessa lies one of the world's most extensive catacomb networks, stretching an estimated 2,500 kilometres under the city and the surrounding countryside. The tunnels began as limestone quarries in the 18th century — Odessa was largely built from the stone cut out of them — and grew into a vast, unmapped labyrinth. Only a small fraction has ever been properly explored or charted.
Tours operate from the Partisan Glory Museum in Nerubayske, about 30 km from the city centre. The guided section covers a manageable stretch, but the experience conveys the scale of the system and the eerie quality of being underground in a tunnel with no natural light. Getting lost in the unguided sections is a real risk — groups of urban explorers have died here — so stick with the official tours.