I've got a list of a few of my favorites, and I'm looking for others to add to it. Mine include:

  1. Horseshoe orbit moons (that if observed while on one of them will look like the other moon is about to crash into you, and then it slowly proceeds to go away)
  2. A small visible galaxy
  3. Planet rings/a gas giant with rings
  4. Multi star systems with each star being a different color (possibly even feeding off each other)
  5. Auroras
  6. Floating magnetic islands with waterfalls
  7. Rocheworld/Ring World/Dyson Ring/Dyson Sphere
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    $\begingroup$ Hello and welcome. Please see help center. Questions where every answer is equally valid are specifically on the "do not ask on this site" list. $\endgroup$ – Mołot Oct 16 '17 at 6:16
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    $\begingroup$ As Mołot said, this question is based entirely upon oponion and as such it will be closed. If you get 20 (I think) rep you can come and ask about it in the chat. chat.stackexchange.com/rooms/17213/the-factory-floor $\endgroup$ – Bellerophon Oct 16 '17 at 6:56