Istana Nurul Iman Palace, Brunei: $3.3 billion (£2.4bn)
Built in 1984 at a cost of $1.4 billion (£1bn), the Sultan of Brunei's eye-opening home is the largest palace in the world that is still in use as a royal residence. The complex contains a total of 1,788 rooms, including a banqueting hall that can seat 5,000 guests.
