From Thimphu, we drive for about three hours to Punakha. Changing climatic zones from mountainous to tropical. On the way, we cross over Dochu La, a 3150-metre-high pass marked by prayer flags and a chorten and, if the weather is fine, a view of the eastern Himalaya including the highest mountain in Bhutan, Mt Gangar Punsum (7520m). We drive through forests of rhododrendron and magnolia, before the road descends into the warmer lowlands around Punakha. We visit the Punakha Dzong, which once served as the old capital of Bhutan. This remarkable fortress was built in 1637 between two rivers and has survived many glacial floods and fire.