Due to excessive groundwater extraction, the Indonesian capital Jakarta and its 11 million inhabitants are sinking below sea level at a worrying pace. This phenomenon has prompted the Indonesian government to take a radical decision: to move the capital more than 1,500 kilometres away and create a new city from scratch on the island of Borneo, in one of the world's largest stretches of tropical rainforest. Lucie Berbey and Ulysse Cailloux report from Jakarta and Borneo on the rationale and challenges of this unprecedented decision.