AdventureCraft is a standalone mod that you can use to create your own adventure maps.
Here is the forum post for it.
It requires that you be running Minecraft 1.2.4, so if you've patched up to 1.2.5 (like any sensible person would) you can just go into .minecraft/bin and remove (OR BACK UP) the current "minecraft.jar" file and rename your "minecraft-1.2.4.jar" file to "minecraft.jar" if you have it. If you don't, good luck finding the 1.2.4 backup file online.
Anyway, the main purpose of this thread is to share maps you've made and/or maps that you found particularly interesting or fun to play. I've created this separate from the Big Ol' Minecraft thread because this isn't exactly about Minecraft, it's about AdventureCraft and its custom maps and such.
To get us started off, I've been playing a rather well-made one called Journey to the Aether. So far, from what I've gathered, it's about a man (you) who finds a way to bring back his long-dead wife and daughter as told to him by an old man (and you should always trust what old men say). I'm going to take a guess and say that the Aether is how he brings them back.