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"Not a dead-end external dwelling," or more accurately, a semi-open one, is permitted in this tournament.
By "semi-open external dwelling" in this case, I mean a place where a unit or Hero can
enter on foot, while the attacking monsters—regardless of their size—must be able to reach the Hero or unit to strike them (the point of a semi-open external dwelling is to limit the number of monsters attacking you simultaneously).
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A "not dead-end" external dwelling is one that a hero can enter, and a small unit can enter, but a large one cannot—which is why the word "external dwelling" is used here. As for what you're writing—that's NOT an external dwelling at all; it's a natural obstacle that prevents the enemy from swarming you all at once.
Consequently—a "not dead-end" or semi-open external dwelling is FORBIDDEN. A dead-end one, obviously, is too. All other clutter is permitted. Personally, this would be clearer to me. Probably for others as well.