Hello Operation Epic Scope Quest friends. I really, really love Epic Megastructures in sci-fi literature, movies and games. Massive planet sized artificial creations, terrifying alien objects of indeterminate origin. Like the Star Bridge or the Rings of Trantor in Isaac Asimov's Foundation. But then I created a list based on books including Megastructures and I got a bit lost in how to define them. Like the Fortress buildings (e.g. Arrakis) in Dune, are they Megastructures? Does it have to be artificially made or not? Planet sized or not? Or how about labyrinthine places, are they a sub-set of Megastructures do you think or are they not 'large' enough?

So basically I'm crowdsourcing to see what you all think out of curiosity!

What do you think of when I say 'Megastructures'?