We often know and recognize the skyline of cities but are completely unaware of what is hidden underground: discover the underground city in the Australian desert, learn about Canada's shopping arcades or New York's spider-web-like underground transport network.

The last page features the most striking and audacious underground constructions such as the Channel Tunnel linking the UK to France.

"'There are several subterranean settlements around the world, and this intriguing STEAM picture book profiles 15 of them ... The illustrations steal the show, laying out tunnels, passageways, and interconnected levels ... With applications across multiple curriculum areas, this book will capture browsers' attention and demand multiple reading'" - Booklist