This book explores how new ideas and technologies can help to make our increasingly dense, climate-stressed cities both more resilient and more of a pleasure to live in. While it sets out practical design approaches, Underground Cities is not a technical manual. Designed for everyone with an interest in the future of our cities, it is beautifully illustrated and written in an accessible style that draws on the rich tradition of underworlds, both real and imagined, in art, history, and poetry. Its ambition: to change the way people think about the underground. Global in scope, the book ranges across continents as it surveys the vast expansion in the potential of the underground. The opening section, "A New Frontier," looks at two pioneering cold-climate cities, Montreal and Helsinki, which developed new uses for the underground from the 1960's on. The closing section, "Looking Forward," offers glimpses of what we might be able to achieve in the next 50 or 60 years. Focusing on Hong Kong, Singapore, and Tokyo, it shows projects that are going deeper, achieving a greater synergy of uses, and paving the way for new urban forms. In between, the review of innovative ideas extends from logistics to pneumatic technologies, from new means of mapping the subsurface to the physical and psychological impact of spending prolonged periods in a subterranean environment. A presentation of buildings and projects by leading international architects and artists highlights the advances in technology that are making it possible to bring the elements of nature-light, air, and vegetation-deep underground.