I like the idea of BFOs/BDOs, depending on what parlance you might want to use [Big Dumb Object… you might be able to guess the “F” version…]. The allocation of resources, the idea that a society would labor so long to develop and construct something (never mind the leaps in technology that could happen WHILE said thing is being built)…what happens when said object is discovered?
Consider the above: What is it? A ginormous hollowed out rock floating through space – or maybe a manufactured cylindrical structure – where the above image is of their…dock? Are all of those structures ships moored to the inside of the cylinder, or actual fixed structures? The arriving ship… is it part of the fleet/related to the moored vessels, or a new arrival? Friend, or foe? What is the purpose of the BDO – a generational ship? A space station? A colony?
Consider, again, the ships (or just a ship, if you want to keep it simple) – do they dock? Pass through (depending on the BDOs design)? Assuming a docking pattern, does everyone stay aboard until secured, or does a small unit [assault team] deploy while in transit?
What’s inside the BDO? “People” [assume ‘sentient race’ if not necessarily humanoid], or is it abandoned? If abandoned, is it empty or a literal ghost town [could it be UF if it’s in a space station? Hmmm…]?
What does it suggest to you? Now, what backstory could build to this moment, and who is the person that gets stuck doing the grunt work of whatever’s planned?