This book offers an uncompromising and unapologetic phenomenological study of altered states of consciousness in an attempt to understand the structure of human consciousness. Drawing on the philosophy of Merleau-Ponty, it sets out to decipher the inextricable link between consciousness, body, and world. This link will be established through the presentation of in-depth phenomenological research conducted with former prisoners of war (POWs) and senior meditators. Focusing on two such disparate groups improves our understanding of the nature of the subjective experience in extreme situations - when our sense of boundary is rigid and we are disconnected both from the body and the world (POWs); and when our sense of boundary is fluid and we feel unified with the world (meditators). Based on empirical-phenomenological research, this book will explain how the body that is from the outset thrown into the intersubjective world shapes the structure of consciousness.