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This is roughly the same as Bald Bear's (first) answer, but more fleshed out... The "ruins" are built (and removed) by "cloaked" repair mechs of unknown origin. These mechs have some form of proba...
Answer
#1: Attribution notice removed
by
System
·
2020-12-01T17:59:13Z (over 3 years ago)
Source: https://worldbuilding.stackexchange.com/a/160339 License name: CC BY-SA 4.0 License URL: https://creativecommons.org/licenses/by-sa/4.0/