It took some time to adjust to the gloom after the bright sunshine outside. I used the weak beam of my torch to look around and suddenly realised I was standing beside a giant foot, around 6m long.
As my eyes slowly adjusted, a huge hand appeared high over my head, as though delivering a giant blessing, then flowing robes and finally, when I craned my neck back to look up, the light through an aperture far above illuminated a giant face.
"This," said our guide, pointing his much more powerful beam at the figure, "is the largest indoor statue in the world."
The scale of work involved in creating this 35.5m Buddha in its cave was mind-boggling. It took 12 years to carve the great smiling Buddha out of the rock 1400 years ago - with nothing more than primitive hammers and chisels.
Then the walls had to be plastered with a mix of mud, straw and some sort of glue, to a depth of 3-4cm. Finally the plaster was been painted meticulously using ground minerals - malachite, ochre, lapis lazuli - as paint.
Yet this is only one of about 500 equally spectacular caves carved into a riverside cliff in the middle of the desert, at Mogao near the Chinese city of Dunhuang, over a period of about 500 years.
It is all said to have started around 366 when a monk saw a vision of Buddha above the cliffs, decided this must be a holy place, and carved the first cave as a tribute.
There is no trace of that cave but it, and news of the monk's vision, inspired others to follow suit and, according to Lonely Planet's China, at its height there were 18 monasteries, 1400 monks and nuns, plus countless artists, craftsmen, labourers, translators and calligraphers all working here.
For centuries the caves were forgotten, except by a few monk guardians, and over the centuries there has been some deterioration from flooding - the river has now dried up - sand from the desert looming at the top of the cliff, earthquakes and oxidisation.
But for the past 50 years or so the Chinese Government has made a big investment in preserving what Lonely Planet describes as "one of the greatest repositories of Buddhist art in the world".
When we arrived at the cave site, and were confronted with a massive concrete wall dotted with hundreds of doors and dozens of staircases and landings, one woman asked, not unreasonably,"Is this a hotel?"
Bin, our Chinese tour leader, burst into laughter. "Yes. It is a very old hotel. More than 1500 years old. These are the caves."
Later our guide explained that the concrete facade and lockable doors had been added in the 1960s to stop the rock face from collapsing, improve security and reduce the deterioration of the works of art.
The amount of art here is extraordinary, as is the range of cultural influences on show.
In the earliest of the 10 caves we were taken to see, dating from the late 5th century - it was cave 259: they're all numbered just like hotel doors - our guide pointed out that the statue of a disciple, standing on the left hand of the 3m high Buddha had Turkish, not Chinese or Indian, features "because Turkish nomads were in control of this area when it was built".
He pointed to influences from Persia - in the style of clothing of a painted Buddha - India, Pakistan, Han Chinese, Afghan - a statue in the style of those at Bamiyan - Mongol, Turkish - in the features of a disciple - and Greece.
In another cave he drew attention to the main Buddha statue dressed in Chinese robes and then, with the aid of his torch, highlighted an amazing conglomeration of religious figures on the ceiling from Hindu gods to Taoist immortals and from Chinese nature gods to multi-headed demons and monsters.
Most ceilings, however, were covered with hundreds of small figures of Buddha - his face black, not due to some racial statement, but the result of the red pigment having oxidised - and the most common wall painting themes were scenes from his life or visions of paradise.
As you'd expect from people living in caves in the desert their paradise was one of comfortable palaces amid lush green parks, ample food and pleasant music.
In one particularly imaginative version the instruments were playing themselves. Often, angels were flying above. But, as our guide pointed out, "These are not like your angels. They do not have wings sprouting out of the middle of their backs. They do not need them."
Every cave contained at least one statue and most contained several. The larger ones were mainly carved out of the rock but the smaller ones were built of earth, straw and adhesive material around a framework of sticks.
Now and again we saw a figure whose hand had broken off but had not yet been repaired, so sticks and bits of straw extended from the shattered wrist.
Always at the centre was the Buddha; in one of several poses, mostly surrounded by a couple of disciples and several Bodhisattva (those who have attained enlightenment but stayed in the earthly realm to help others).
Several had guardians at the entrance, ferocious snarling creatures whose frightful appearance was aimed at scaring away evil spirits. I'd have thought they might have made cave robbers a bit twitchy too.
There were other giants figures, too, besides the world record holder. In one cave, which echoed to the sound of of drilling and banging - "they're building a better viewing platform at the other level" - there was a 27m-tall Buddha in whose cave archaeologists had found silk banners saying it took 29 years to sculpt.
In another, outside which two fearsomely tusked guardians growled, a 15m-long Buddha lay at rest, eyes closed in peace, having attained nirvana. It was built in the 8th century but a line of around 70 mourners behind the giant figure, each with the features and clothing of a different race, were added in the 19th century.
But remarkable though all these carvings and paintings were, the greatest treasure in this great complex was found when a monk cleaning a fairly nondescript 9th century cave discovered a small, bricked-up side room.
Inside were 50,000 manuscripts, mostly containing ancient Buddhist sutras, but also everything from poems and histories to medical recipes and biographies, enough fascinating material to found a whole new branch of study called Dunhuangology.
However, as our guide pointed out bitterly, Western archaeologists were quick to hear of this find and sweet-talked the hapless monk out of most of the papers. Today, only 8600 manuscripts from the hoard are left in China. A few are on display in the Dunhuang Museum and in national institutes in Beijing.
"The rest are in Britain and Europe and the United States."
I could have pointed out, but didn't, that reprehensible though that cultural larceny might have been, at least it prevented the documents from suffering the fate of the millions of ancient relics destroyed during the madness of the Cultural Revolution.
As our tour of the caves ended, one of our group asked where the people who built the caves lived. "Did they live and work here?"
"Oh no," said the guide, "these were sacred places. They lived in another group of about 300 caves further north.
"Those caves are not open to the public because they are still being excavated. Already they have discovered two pages from the Bible written in Syriac, two Nestorian crosses and a Persian coin from the 5th century BC."
It all served to underline what a crossroads of civilisations this place was when the Silk Road was at its height and Dunhuang was a vital oasis for travellers through this arid landscape.
Indeed, the harshness of the next leg of the route, westward through the terrifying Taklamakan Desert, evidently played a big part in the caves being built, according to the guide.
"Some people gave money in the hope the gods would allow them to survive the Taklamakan. Others gave money in gratitude for having crossed the desert safely."
And, sure enough, round the bottom of many caves were lines of painted figures who turned out to be the sponsors: the monks, traders and devout business people who provide the funds for the cave's construction. If it was today, I thought to be myself, logos of beer and tobacco companies would probably be painted there.
My special souvenir of a pilgrimage down the route of the Silk Road through China is a rather magnificent chunk of yellow rock.
I acquired it when I was wandering the streets of Dunhuang taking photos of the replicas of artworks from the Mogao Caves, which the proud citizens have erected on blank walls, street corners and open spaces.
You're not allowed to take photos inside the caves so I thought pictures of these official replicas would give a slight idea of what the amazing artwork is like.
During my fairly brief stroll I came across wall paintings of court scenes and visions of paradise plus sculptures of angels and heavenly musicians.
The best was a huge statue - taken from one of the cave paintings of paradise - featuring a beautiful young woman playing a lute behind her back.
When we first saw her, Bin, our group leader, commented drily, "I think that must be very difficult."
Later, in the caves, I found that very figure in the 8th century cave 172.
But while I was going about this photographic exercise the local schools closed to allow pupils to go home for lunch and I was soon surrounded by a mob of giggling youngsters who obviously hadn't seen a lot of round-eyed people, even though most of them spoke a bit of English.
One cluster of boys, aged around 10 at a guess, stared in fascination at the notes I was taking in a small notebook and when I turned the pages towards them so they could see my cramped script they just about collapsed in giggles.
Several more came up to say "hello" and there were lots more giggles when I replied "hello" and, especially, when I tried a tentative "nihao".
One boy then came up with his hand extended and said, "Hello. Here, something for you," and he handed me the rock.
When I took it and said "thank you" he beamed in delight and ran off with his giggling mates.
I've kept the rock and brought it home. I think it's rather splendid.