What do you see, hear and experience when you drop miles into the deepest parts of the ocean? For journalist Susan Casey, it was transformative — even emotional. Her latest book, “The Underworld,” is a homage to the abyss and the scientists who explore it. She also describes her own dives in deep-sea submersibles, through the oceanic “twilight zone,” which is rich with bioluminescent creatures, down to depths of 5,000 meters, where utter darkness still teems with life. Casey joined MPR News host Kerri Miller on this week’s Big Books and Bold Ideas to share stories about her dives and what she experienced in the abyss. She also talked about how the deep submersible community reacted to the tragic end of the Oceangate Titan sub last summer (“people were watching the creation of that sub with real fear”) and warns of the growing interest in deep sea mining. Guest: Susan Casey is a science journalist who specializes in writing about the ocean. Her latest book is, “The Underworld: Journeys to the Depths of the Ocean.” Subscribe to Big Books and Bold Ideas with Kerri Miller podcast on Apple Podcasts, Google Podcasts, RSS or anywhere you get your podcasts. Subscribe to the Thread newsletter for the latest book and author news and must-read recommendations.