Anna Karenina
Anna Karenina is, succinctly, a book that talks about the unhappy marriage and subsequent affair of a Russian society woman in the late 19th century. That description is accurate in a way, but misses what the book really has to offer. I think it's better described as a book that teaches how messy things can get among people in society, even when everyone's acting the way they ought to, or the way they feel they have to.
Anna is married to a husband that is much older than her, a common enough situation at the time. She can't relate to him, and grows to resent him when she falls in love with someone that she has a deep connection with. Her child is caught in the middle of a bitter divorce, her husband is relegated to letting his wife go against his will despite cherishing what they had, and she, who could not have stood to do anything else, is aware of the hurt that was created by her actions. None of this was helped by the social disgrace around divorcing at the time, which complicated things further.
After a "honeymoon period" of blind love, reality creeps into Anna's relationship with her new not-legally-but-pretty-much-husband Alexei Vronsky and they find tension building between them. With them having sacrificed so much to be together, there's a pressure for their bond to remain perfect, untarnished. But it doesn't work out that way.
It's all rather sad, and deeply so because it's a believable story.
While the book's titular character is important, Konstantin Levin is a co-protagonist. I enjoyed reading about his journey to finding satisfaction with both his roles in life and his spirituality. His epiphany at the end of the book is what really stuck with me, and it's ironic, since it's hardly tied to the Anna Karenina plotline at all.