cd

If you don't know what the parent folder's name is, but you do know the child folder's name is, you can use cd */foo to get there.

Examples: I'm in a ports system (OpenBSD, Gentoo, etc), and I know I'm looking for package name mplayer, but I don't know what category it's in:

cd */mplayer/

If two of the same child directories exist in more than one of the parent folders, then cd will go into the first one it finds.