What is known about Rub' al Khali, one of the world's most dangerous deserts?

An Indian man died from exhaustion and dehydration after getting lost in Saudi Arabian desert Rub' al Khali. Known as one of the world's most dangerous deserts, it stretches over 6,50,000sq km and is notorious for its extreme climate. Annual rainfall in the region is less than 50mm. The term 'Khali' signifies complete emptiness, with nothing in sight for miles.