How do unmarried women with no mahram go on a pilgrimage to Mecca?

A pilgramage to Mecca is one of the five pillars of Islam , considered mandatory for both men and women. However, Mecca is in Saudi Arabia, a country which enforces strict rules on the behaviour of women. One such rule in Saudi Arabia is that a woman is not allowed to travel without a husband or a mahram . It is, however, possible that a woman might have no husband nor (living) mahrams. **Q**: How can an unmarried women with no mahram complete her pilgramage to Mecca?