A walk around Hackney with Josh Bilton and urban geologist Ruth Siddall to learn more about the geology of the land and the built environment. The walk is a psychogeological response to Bilton’s Cairns – the walking aspect of his SPACE commission, Undersong. It explores the geology, conceptions and perceptions of Portland Stone in London’s architecture and culture. Ruth Siddall’s amazing knowledge of geology brought the urban landscape to life in a way that I have never appreciated before.