The Story of Buildings is simply one of the best intro books on architecture we've found.
Admittedly, it's targeted at a junior crowd, maybe ages 10+, but that just means you get a lot more great pictures and diagrams than in for-adult books, and good-sized letters that won't have you squinting.
The book is full of great info and stories about famous buildings and movements. It follows a historical trajectory, placing major architectural movements in the context of history, for example, using the Crystal Palace in London to highlight how the industrial revolution completely changed the way buildings could be built, or discussing the Baroque period in light of the Reformation and the Catholics differentiating themselves from the Protestents.
And it passes-on to the reader a little structural engineering intuition about how concrete compresses well, but can't bend, and the brilliance of reinforced concrete is it fixes that. And of course, the wisdom that when you build a house out of legos (I mean, uh, bricks), you want to stagger the bricks across corners for a more robust house.
Some other great architecture for lay-people books we'd recommend:
101 Things I Learned in Architecture School (this is a great series)