Is there any (easy) way to make a terrain which can be edited at runtime? Maybe you know how this is made in Sims 3. There you have a tool for making the terrain higher, one for making it lower, and another tool, which you can use to brush many textures on the same terrain. (I hope you know it from Sims)

i dont know what you exactly mean, but what about freeworld3d (cheap)? you can paint different layers and see it directly?
but i think every other terrain editor does it the same way.

What i mean... imaging there is an entity in the game which walks arround. And everywhere it walks, the ground below this entity becomes green (for ever). Is know clear what i mean?

Oh yeah, but this feature is available in Sims2, either.
And his question are very clear. But sadly, i don't know how. I just wanted to say that.

It would be VERY nice if that's possible, because I'm making a tower defence game and the first enemy which walks across the path should brush the floor so you can see the path.
If anybody knows a way to do this or has any idea please tell me