Our five pairs set off on a race to Singapore without taking a single flight. They leave behind their smartphones, internet access and credit cards. All they have is the money that the air fare would have cost.
The five teams head out of Delphi to their next checkpoint - Baku, the capital of Azerbaijan - a journey that sees them leave behind the familiarity of the west.
They depart Baku, the capital of Azerbaijan, on the third leg of the race - taking them across the vast deserts, mountains and Silk Road cities of Central Asia to the ancient capital of Uzbekistan, Tashkent.