You could walk from London to Edinburgh and back (twice!) in the time it would take to explore the entirety of Odessa’s underground tunnel network. But you wouldn’t need a hard hat, or pass through a Soviet cold war bunker, or walk the plank over roughly hewn, slippery stone, or admire underground street art or be enchanted by a cave pool glowing blue, red, turquoise and yellow in the gloom.

By some accounts these are the most extensive catacombs in the world, stretching some 2500km, though it’s hard to fathom who might have explored and mapped them all. A sign bolted onto the glistening limestone walls explains that, in contrast to more famous catacombs in Paris and Rome, Odessa’s tunnels were not used to bury the dead (so technically they were not catacombs at all).

Instead, it was the limestone itself that inspired this labyrinth. Catherine the Great founded the city of Odessa in 1794 on the site of a sleepy fishing village; it expanded rapidly from a few shacks to become imperial Russia’s second largest port and its main grain distribution centre, garnished with magnificent public buildings in renaissance and classical styles, including the world-famous Opera and Ballet Theatre. This construction boom required prodigious quantities of stone and, as luck would have it, it lay waiting underfoot and so a frenzy of tunnelling ensued. As ever more ornate buildings arose above ground, so too did Odessa’s underground realm expand in equal measure, an ugly reflection perhaps but a reflection nonetheless.

Yet who among Odessa’s citizens would ever have visited this shadow world except for the unfortunate souls chiselling away under flickering kerosene lamps, oblivious to night and day? And who among those stone miners might ever be invited inside the buildings that they had carved from the earth?

Mining eventually ceased, but Drama and Tragedy still crawled through the tunnels, and legend mingled with fact in the gloom. For sure we know that partisans resisting the Nazi occupiers spent months underground before turning on each other, whether through hunger, madness or desperation, until only one man remained. This downward spiral is recounted in harrowing detail in a series of letters from one of the partisans to his wife until in the last letter he refers to his impending demise; extracts from the letters are bolted to the very stone that constituted both his shelter and his prison. More recently, there have been claims of citizens getting lost or murdered down there, with their remains being discovered much later. We asked our guide who, with a wicked glint in his eye, reckoned that two or three people per year met this fate.

Whenever I lagged behind the group to take pictures free from tourists and once their torchlights and voices had faded, I soon felt alone in the world and, fearing I might become another statistic, hastened to rejoin the group. However, at certain forks I was uncertain which way they had gone and, straining to discern faint echoes or flickers of light, it became all too apparent how quickly bearings might be lost in this Google-free, featureless labyrinth. That night, I was haunted by a vision of myself taking a series of wrong turns, energy levels and torchlight diminishing with each misstep, and hope transmuting into defeat, resigned to eternity in the bowels of the earth. For the unlucky souls that had experienced this for real, the Odessa tunnels were as much a place of burial as the Rome and Paris catacombs after all.