The Empty Quarter (Arabic: الربع الخالي, Rub'al-Khali) is the large, expansive desert encompassing a large part of the Arabian Peninsula. It's the largest continuous body of sand in the world.
One may be tempted to call the Empty Quarter "no man's land", but that's not entirely correct; various local tribes are based here. The Saudi borders with the United Arab Emirates, Oman, and Yemen are situated here... somewhere, but nobody has bothered to actually draw those lines in the sand.
In 2006, the Saudi government organised an scientific excursion in the region and they came across various types of fossilised creatures and meteorites.
If you do encounter people here, your best bet for communication is Arabic.
A caravan of 4WD vehicles or camels are the only sane options for entering the soft sands of the desert.
On paved roads, in the UAE, a road passes through the oasis towns, and a drive is possible to Tal Mireb, the tallest dune in the country, which gives a few minutes of perspective on how vast and inhospitable this place is.
The Empty Quarter is all about nature and wildlife. Expect to see a lot of sand.
You can drive around, or, if you're feeling adventurous, you can walk around.
There are no restaurants in the region. You have to carry your own food.
You should carry lots of water with you.
Luxury hotels at the edge of the Empty Quarter can be found in Liwa Oasis, UAE.
Never, ever drive alone, even if you're an experienced driver. Much of the Empty Quarter is barren and you can get easily lost if you don't know what you're doing. For all you know, you can unexpectedly end up in a completely foreign land and you may find it difficult to get back to where you started.
Another danger is the extreme, arid heat. Carry lots of water with you, make sure your vehicle can handle the harshness of the desert, and make sure you have a reliable communication device in the event you get into trouble.