I've always thought that I had a reasonably comprehensive vocabulary. I've learned much through reading, which has led to many embarrassing mispronunciations, but hey, it's good for my ego and all part of learning. It's not often I come across a word I'm unfamiliar with, but when I opened District and Circle (a collection of poems by Seamus Heaney), I had to read it with a dictionary by my side!
Every third poem or so I'd check a definition and my eyebrows would raise as a sentence came to life. The frequent interruption didn't detract from the experience, somehow having to strive for understanding made the reading richer. I love the choices Heaney makes. The rhythm of his sentences and the vivid imagery he conjures in my mind, make him my favourite poet... (Not that I'm terribly knowledgeable or well read.)
I heartily recommend District and Circle. The words of it's title poem in particular have stayed with me. Heaney's observations and perspective of the world we live in, has broadened my own in a small but beautiful way.