What is the world's largest continuous sand desert?

The Rub' al Khali is the world’s largest continuous sand desert. Its name means “Empty Quarter,” and the desert covers roughly 650,000 square kilometres across Saudi Arabia, Oman, the United Arab Emirates, and Yemen.

It forms the southern part of the Arabian Desert and stretches about 1,000 kilometres from west to east. Much of its surface consists of vast dune fields, with some dunes reaching around 250 metres high, although gravel plains, salt flats, and gypsum-covered areas also occur. The sand’s reddish-orange colour comes partly from feldspar minerals.

The Sahara is much larger overall, but it is not one uninterrupted sea of sand: large areas are rocky or gravelly. The Rub' al Khali is therefore the standard answer when the question specifies the largest continuous sand desert. Its hyper-arid climate historically made travel extremely difficult, although ancient frankincense trade routes crossed parts of the region before desertification intensified.