Max Tegmark has an unusual idea: reality is just a mathematical structure. This is a bold claim about reality, so to get those of us there, he walks through a journey of what we know about our universe and how we know it. More importantly, he builds to focus on what the same mathematical underpinnings we use in our universe predict about things we can't directly observe.
To get anywhere close to explaining his ultimate theory, he spends sufficient time explaining the cosmos, with successes and failures of previous theories, so even a non-academic can understand where multiverses came about.
Part “introduction to the cosmos”, part memoir, part philosophy, Tegmark's journey is brilliant and enjoyable. The most meaningful portion for me was a metaphor he offered for life. I'll write more about this later.