The Rub' al-Khali (الربع الخالي) or Empty Quarter is the largest sand desert in the world. It covers most of the southern third of the Arabian Peninsula, including much of Saudi Arabia and areas of Oman, the United Arab Emirates, and Yemen- some 250,000 sq miles in all.
I was there to visit Shaybah, a major crude oil producing site in Saudi Arabia located approximately 40 km from the northern edge of the Rub' al-Khali. Shaybah is home to about 1000 permanent workers, with tens of thousands of contractors at any give time also working the site- all men of course.
The desert was just unbelievable though sadly since the day was hazy, the sands don't appear as red in many of the photos as they did in real life. I've heard that on a clear day, when the sun starts to set, the dunes seem to catch fire with color- a magnificent site I am sorry we missed (though moonrise was pretty cool). Nevertheless, I am thrilled I was able to make it to the Rub' al-Khali before I leave Saudi Arabia.