We were doing it more and more, anyway. Mindfulness and meditation are all the rage. Wellness tourism, yoga breaks, meditation apps, and spiritual boot camps have been booming - entry-level to hardcore.

Retreat investigates this human obsession, mining neuroscience, psychology and history to reveal why we seek solitude, what we get out of it, and what is going on in our brains and bodies when we achieve it. What has it meant to the world's great thinkers, and what does it mean, in our age, as an activity we pay for?

Is isolation a means of engaging more fully with reality, or evading it? And what has retreat meant at a time when humanity has - to an unprecedented extent - been forced to withdraw? Nat Segnit has felt the pull of solitude and the fear of it, as well as the warmth of company. To answer these questions, he has been on retreats around the world and met yogic scholars, cognitive and social scientists, religious leaders, philosophers and artists.

Retreat is endlessly enlightening, sceptical and open-minded. It is about seeking happiness, fulfilment, a change of perspective, and relief from stress and anxiety. And it is surprisingly, joyously, full of human encounter. Ultimately, it is about the discovery that retreat is a mental state that can be achieved anywhere, in a monastery or shopping centre, a cave or a crowd.