Previous civilizations are a cool idea, and it would make scientific sense Any where there is water life is gonna (to our knowledge) pop up, including Intelligent life.
Why not have an abandoned Planetary defence base, Heck even have ab…
Don't know if you Devs have though about it or not, and I don't know how well it would fit, but an actual means to defend yourself would be grand, To fit I would say non lethal, like a stun cannon or something that knocks baddies Completely out, …