The question is incredibly vague to me. All books that you find interesting or that you simply have <i>fun</i> reading are worth investing your time in. So I could mention wonderful classics of literature. It sounds like you want "insightful" books in a philosophical sense.<p>To those who mentioned Marcus Aurelius's meditations, I recommend the reading of "Zen mind beginner's mind". Along the same lines of somewhat spiritual books, "Siddartha" is a classic and also Khalil Gibran's "The Prophet".<p>Very different: for my personal history, reading "Goedel, Escher, Bach" when I was 18 deeply affected my vision of things. Other science books I loved: "the unfolding of language" (historical linguistics) and "the world within the world" (physics and philosophy of physics).<p>For something much more recent, that changed my view of the contemporary world, I recommend "Factfulness" by Hans Rosling. It's about understanding "poor" countries in their variety and in a less stereotyped way, but especially about understanding that living conditions <i>across the world</i>, essentially without exception, have <i>massively improved</i> over the last century. I feel Rosling's is only part of the story, though, and "Sapiens" (mentioned by others below) tells parts of the other half.<p>I also like poetry, and in the rare occasions I am in the right frame of mind and focus to read poetry, it feels like a powerful meditation or prayer.<p>If you want to "expand" your vision of things, one thing I tried to do, and loved, is reading as much as possible books from other cultures, for example postcolonial literature. I particularly liked Chinua Achebe's "things fall apart". Somewhat related, "the moon and the bonfires" was deeply moving to me, the life of a man in agricultural Italy after ww2. The reason why I put these together is that they do something extraordinary: we are used to descriptions of africans during the colonization process, or of poor Italians after the war, but we are not very used to them being full three-dimensional characters, <i>people</i> like us, and stepping in their shoes.<p>Finally I enjoy travel books, for similar reasons. Among my favourites is "the road to Oxiana", written in the 1930s, and full of british humour. Also, Rory Stewart (british politician, diplomat and academic) walked Afghanistan in 2002 and told the story in "The places in between". Very, very helpful for understanding Afghanistan beyond the news.<p>I could go on forever!