Secondary features that massively elevate a game for you. Which are they?

[StrixLiterata]

Often games have minigames or side mechanics which have little to do with the main gameplay loop. Sometimes, these can be a joy in themselves and elevate the whole game.

The one I have encountered are:

• The musuem in A House of Many doors, which can house any noteworthy trade items you come across in your journey, and depending on them can become famous for it's beauty, scientific significance, or occult reputation. In similar games, like Sunless Sea or Sunless Sky, I found myself stashing items I didn't immediately need in case they were useful for a trade contract or a quest later; in A House of Many Doors, finding something new had me going "this would look great in my collection".
  In my opinion most open world game swould benefit from this feature, if it makes sense within the world.
• The ability to record and rewatch battles in Total War games, Warhammer 1 & 2 especcially. When you're actually fighting them, you got to take a eagle's eye view of the field and keep shifting your attention, but in a replay, I just love being able to watch the big monters animate and crush, infantry crash and push, artillery firing...
  I wish all strategy games had this feature to let the player sit on their back and properly enjoy their victory.

[Emby]

minecraft fishing. No minigame, just push button get fish. no clue why it's so satisfying but I will literally just build a little shack to sleep in and a dock to fish from with a couple chests for fish and loot and that's basically it.

[BTGBullseye]

Valheim: the way it's designed to require actual support for structure pieces.