Good introductions to different topics?

Someone asks you, hey, I want to get into this thing you're really into, what's a good book to start, what book do you give them? I'm more interested in breadth than depth, something that would cover any glaring gaps in my knowledge that might tell someone "this person knows literally nothing about this", while giving me a lot of jumping off points to pursue in proper detail, the kind of book that has you downloading ten more books while you read it. Terry Eagleton's Literary Theory or HG Wells's A Short History of the World are good examples.

I'm interested (or interested in being interested) in any topic, but books on scientific fields, different artistic mediums, and architecture are especially welcome!