Maps of Europe's most active volcano are continually out of date. Contours shift with the movement of molten rock - as Martin Redfern discovered when he joined a geologist and his team of students, surveying the changing landscape.
Etna is not like the neat, conical volcanoes you see in Japanese woodcuts.
It has multiple craters around its summit and countless cracks and fissures down the flanks.
From these, over the centuries, have erupted lava flows, sometimes destroying villages but eventually yielding the rich, fertile volcanic soils that attract people back to plant new orchards and vineyards here.
Etna is also a big volcano, more than 30km (19 miles) across at its base, and the tourist maps, showing a single road up the flank, are deceptive. We wound our way up a labyrinth of branching, narrow lanes before we found our bed for the night.
We were there to meet Dr John Murray from Britain's Open University and his team of student volunteers. He has been monitoring Etna for 39 years.
As darkness fell I began to be concerned, doubly so as dinnertime came and went.
Eventually, during a late meal, and with the linguistic help of our patient host, we established contact with the scientists who had been delayed, trekking across the lava fields as night fell.
We also discovered that there are two bed and breakfasts with the same name. And yes, ours was the wrong one. But too late to change now. And then the lights went out. "Oh no not again," said our host. Apparently the phone lines had already been out for weeks.
Come the dawn, as he guided us out of the labyrinth, he showed us the remnants of the telephone cables hanging from the tops of telegraph poles where they had been cut, presumably by an organised gang, to sell the valuable copper for scrap.
But back on the volcano, it was a beautiful clear day and time to put on sunscreen.
John Murray is just as you might imagine a field geologist. Wiry, bearded and with a faraway look as if scanning the horizon for eruptions. He seems to know every crack and fissure, every lava flow and crater.
Steam vents from Mount Etna's almost constant eruptions
Using sophisticated GPS satellite surveying systems, accurate to a few millimetres, he measures the mountain as it breathes in and out, swelling as molten rock rises within it, subsiding again after an eruption.
All the maps are out of date, he says, and the height of the summit, 3,330m (10,925ft) give or take, changes every year.
The various surveying points set up on the mountain have been given strange and sometimes rude names by the students. The one we were setting up was called clenched buttock, though I am told it was singular only because of the shortage of characters on the GPS display.
In May this year, after brief fireworks at the summit, a new fissure opened on the east flank and has been erupting ever since.
We trekked over the jagged boulders that litter the steep slope to see it.
Fireworks accompany the eruptions
They call this sort of terrain "aa aa lava". I am told it is a Hawaiian term, but it could equally well be from the expletives uttered while struggling to cross it.
We reached the fissure, encrusted with sulphur and steaming steadily. We felt its heat.
But the actual molten lava was beneath the surface, emerging much further down the impossible slopes.
So we headed for one of the summit craters.
Now, I am not keen to report from a war zone, but the hazards here looked comparable. The difference is that no one is trying to shoot at us.
The volcano is wonderfully indifferent to human presence.
Hard hats and gas masks are advisable. Sulphurous fumes are constantly gusting around the summit and the slopes are unstable. Eruptions up here often take the spectacular form of fire fountains. Great to watch, but stay up-wind and vigilant.
John Murray remembers watching such an eruption from what he thought was a safe distance, only to realise that the volcanic bombs were landing behind him as well as in front.
A hard hat may protect against small shrapnel, but would not be much use against rocks the size of cars.
Thunderstorms are also a real and frequent risk. "But don't be too worried," says John, "I have been coming here for 39 years and I have only been struck by lightning once."
This time the sky remained clear. But, in spite of avoiding the poisonous gas clouds, by the time I reach the lip of the southeast crater, I am gasping for breath.
It is a seriously high altitude. I drain my small plastic water bottle and replace the cap. It is only when I am back home near sea level that I notice that the pressure difference has squashed the bottle flat.
The thin air inside still has a faint smell of sulphur.
From Our Own Correspondent was broadcast on Saturday, 15 November, 2008 at 1130 GMT on BBC Radio 4. Please check the programme schedules for World Service transmission times.