There are tunnel entrances that only give a map of the tunnel system it seems. You can exit that screen by clicking the entrance you have just used. Anything else that can be done there?

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When you find other tunnel entrances their names will appear on the tunnel map. So that
when you enter one tunnel, you can click on the name of another tunnel and be
transported there. It speeds up travelling through the world.

Just make sure that anytime you find a tunnel that you enter it, even if you just click
on its own name so that you stay where you were. But if you don't enter it, you don't
"clear the obstructions" blocking it, and hence don't make it useable in the future.

Make sense?

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Shoot 'em with everything you've got. If anything still lives, shoot 'em again.