Remember: It costs at least 75 bottlecaps to heal and 100 caps to heal Rads. There are a few places of interest that might come in handy when you are getting further into the game unless you blow up Megaton, in which case you need to live in Tenpenny Tower, a smaller and less complicated place. The live atomic bomb is also considered to be a message from the god, Atom, for some (mainly the cult that lives just over the puddle in a church.) Megaton is built inside a small crater possibly created by older atomic bombs that landed there before the currently standing one.
It probably got it's name because of it's giant atomic bomb in a small puddle just in the middle of the town. Megaton has, as i just said, giant metal walls surrounding it's outer parts. Outside is a robot named Deputy Weld, a friendly protectron who always greets your arrival when you come back to Megaton.
It is built in a crater with giant metal walls as protection. Megaton in Fallout 3 is a pretty simple, although complicated town.
