I'm building my little base so that I can see around where I'm currently located at night, so see whether it's safe to go out the next morning, etc. I'd like to make my outer wall out of glass for this reason.
In order to keep Creepers from being dangerous while viewing from inside the base, however, I'm planning a two walled base. The outer wall keeps creepers far enough away from the player (who is confined to the inner wall), such that so long as the player is anywhere inside the inner wall, the creeper cannot detonate.
In order to do that, I need to know how much space to leave between the outer and inner walls. And in order to do that, I need to know what the creeper's activation radius is.
So... what is it?