Paris's underground world of the dead became the setting for an unexpected goodbye

Au revoir, ma mere. Je t'aime.

I panicked. "What's he doing?" came an American voice about five heads back. "He's taking forever!" Quite why there was a queue forming behind me, I was unsure. There was plenty of space around me to access the 112 steps back to the surface. I'd waited patiently for the previous user to trace her message in the digital guest book, where departing visitors are encouraged to pay their respects to the six million souls currently resting beneath the streets of Paris.

Meanwhile, behind me had materialised one of those lines of people who don't know what they're queuing for yet stand there impatiently to find out. So, I gave up my attempts to compose a touching farewell message to my mother, who had passed away four days previously, and scribbled a few simple words of half-remembered school French.

The extensive catacombs of Paris, a dank maze of passages stacked with the bones of centuries' worth of dead, are probably not the best place to process the loss of a parent. I'd booked the tickets a week previously, minutes after they were released for sale, a ploy designed to prevent the attraction selling out months in advance.

I couldn't know my mother would succumb to the insidious black tentacles of transitional cell carcinoma in the intervening week. Bendigo was 10,000 miles away; I couldn't have been any further from her side. The catacombs kicked off a final day roaming the boulevards and boulangeries of the city before my evening flight back to Australia. And now, a funeral.

After a headphone-delivered history lesson lasting half a kilometre, we entered the ossuary, atmospherically lit and respectfully attended by the well-spaced visitors. Long bones were stacked against both walls, joints outward, with interspersed skulls forming decorative patterns - crosses, hearts ...

The founders of Paris had seen no problem with quarrying high-quality Lutetian limestone from deep underground, then using it to build huge palaces atop the voids their extraction had created.

After 600 years of use the tunnels began to collapse and the operation was finally abandoned in 1776. Ironically, the French word for foresight, prevoyance, was coined around the same time.

My travelling companion Geraldine and I meandered along the galleries of deceased, from paupers to nobility, upstanding citizens to castigated villains (Robespierre is down here somewhere). A subterranean tunnel of bones is a polarising tourist attraction. I need not extol its virtues here; you're either coming next time you're in Paris, or you aren't. Improbably for an Englishman, I've never actually spent any meaningful time here before so this has been on my list for 20-odd years. But then I'm the kind of guy who has stylised skulls on all his clothing, here in France to attend a four-day metal festival called Hellfest.

Around the same time as the quarry closure, the city's cemeteries were declared full, some having been in continuous use for a millennium. Cadavers were bursting through the mud into neighbouring cellars, much to the surprise of their owners, and in 1777 a decision was made to repurpose the (consolidated) mining tunnels into the world's largest ossuary.

A 30-year exhumation/reinterment project was initiated, taking place at night to prevent horrifying any passing public, and six million souls were transplanted to their (final) final resting place.

Thirty years later the site was opened to the public, allowing the living to pay their respects to their loved ones.

Once back in fresh air we elected to walk through the Jardin de Luxembourg, past the Sorbonne and the Pantheon to Notre Dame, a trail to fill the heart of any antiquarian. But first, the famous Cemetery of Montparnasse - a strange choice, I grant you. Maybe I just felt more comfortable among the dead that day.

As the ridiculousness of her words dawned on me, I started laughing and could not stop. Two minutes, five minutes, 10 minutes ... I was incapacitated, could barely walk. I mean, it was funny - did it take her that long to notice we were in an area the size of 25 soccer pitches literally dedicated to tombs? - but not that funny. Thank you, catharsis.

As the giggles died away and I regained my breath, I reconsidered my rushed epitaph. I guess it wasn't so bad. Simple, direct, honest. In fact, given more time I probably would have overcooked it. Now those five words would be lodged in the servers of the City of Paris, hopefully forever. I just wish I could have said them to her face.

"Goodbye, mother. I love you."