Favorite kanji?

[Sakurahime]

One of the interesting parts of about Japanese, as a native English speaker, is kanji. Simple and complicated at the same time, these pictographs can hold a wealth of information, from meaning to pronunciation. And they can be put together in a number of ways to create completely new meanings! I wanted to share my interest and gather people's favorite kanji and kanji words. Maybe we'll all learn something new, too I've also created a thread about favorite words, if anyone's interested in that as well.
So, to get us started are a pair of kanji that I really like, found by my friend. Their meanings are concave and convex, and they really are the perfect visual representation for this: 凹　and　凸 !
And for a kanji word, one of my favorites is 自動販売機 (jidouhanbaiki). It means vending machine and literally says "self/automatic selling machine".

[Sakurahime]

I've got some, if anyone is interested... First, some single kanji! Take a look at these, and see if you can guess what they might represent: 上　下
Any ideas?
Here's a clue: they're directions.
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...
If you said "up" and "down", you'd be correct! All I think of when I see them are plants. Up goes the stem, and down go the roots. They're useful kanji when you're trying to find the right escalator in a department store!

Second, another kanji word: 図書館. I'll just tell you this one; it's "toshokan", which means library. The first two characters together mean "books", and the last one means "building". Ta-da! It's a book building! The character for building can be found in plenty of other words, too, like "movie building" 映画館 (cinema!) or "old things building" 博物館 (museum!), and even "beautiful things building" 美術館 (art gallery!)