Hidden among the Idehan Ubari - the Ubari Sand Sea in south-east Libya - are some of the most extraordinary sights to be found in the Sahara.
I have seen photographs but nothing prepares me for the view when our four-wheel-drive stops on the crest of a sand dune. The slope falls away in front of us down to an extraordinarily deep blue lake fringed with palms and flowering grasses.
The contrast between the palette of sands whose golden colours change subtly with the play of sunlight upon them, is breathtaking. This is Gebraoun, one of the three Ubari lakes that still have water - many others have sadly dried up over the years.
On the southern shores a sand dune rises up hundreds of metres but on the flatter northern bank is a small camp for visitors.
Mostly fashioned from date palm fronds, the encampment contains a shaded restaurant area, a changing hut and several shops where Tuareg salesmen entice visitors to buy their silver jewellery, daggers and stone carvings.
Once there was a thriving village here - the inhabitants traded tiny shrimp from the lake with passing Tuareg caravans in exchange for goods such as olive oil. Their shrimp diet led to them being known as the Worm Eaters.
It might be winter and time to wrap up for the locals but the sight of water in the arid desert is too much to resist for visitors. Covered up as discretely as possible in a sarong, I venture gingerly into the water.
There's a faint smell of sulphur. I tell myself that the "worms" really were shrimps and not some horrible desert creature that is going to burrow under my nails or worse.
At home I'm used to swimming in lake, river and sea water that is sometimes at least tepid for the first centimetre and then freezing.
So I'm startled to discover that in Gebraoun the cool surface layer is sitting on top of water that gets hotter the deeper one gets. It is also extremely salty - creating almost as much buoyancy as the Dead Sea in Jordan.
I float, staring up at the sand dune and listening to the Arabic pop music that is blasting out of a hut further down the lake.
Every now and then there is a burst of singing and clapping - it turns out to be a group of Syrian men on holiday.
After 20 minutes in the water my skin is slippery to the touch and my mouth is stinging from the salt. I make a discreet exit (Libya is a relatively conservative Muslim country and women in bathing suits are not a common sight).
My sarong dries in the sun and when I come to pack it later it is as stiff as cardboard.
Tuareg are floating decoratively around the camp in their blue robes, all but their eyes swathed in turbans in traditional style. Some are selling traditional silver Tuareg crosses - each tribal group makes a distinctive design.
What is not quite so traditional is the collection of skis and snowboards leaning against the kitchen hut. For a small fee one can hire these and ski down the sand dune above the lake.
We leave Gebraoun for another of the lakes, Umm al-Maa, that is even more thickly fringed with vegetation.
The desert wind has disappeared and the dunes on the far bank are reflected almost perfectly in the limpid waters.
Our caravan of four-wheel-drives presses on along a wadi that winds its way between meandering ridges of sand.
A desert fox trots out of our way and Sa'id stops to show us snake tracks... there are camel hoofprints too.
He parks on the summit of a sand mountain and while we stand there in the late afternoon sun, a man in full-length robe materialises from nowhere walking carefully along a ridge. Even our drivers have no idea where he has come from.
It's the stranger's turn to look surprised when I and a few of my group decide to run down the dune.
I descend in bare feet - brushing off thoughts of deathstalker scorpions and sand vipers.
The sand is cool, silky - I have the Sahara between my toes.By Jill Worrall