What are the effects of discovering a natural wonder?
In Civilization 5 discovering natural wonders had a powerful effect (+1 to global happiness). In Civilization 6, when I discovered a natural wonder, I also seemed to receive a religious relic. That leads me to wonder if the effects of discovering natural wonders is different in civ 6 than civ 5.
What are all of the effects of discovering a natural wonder in Civilization 6?
There are 12 Natural Wonders in the game.
The discovery of a natural wonder gives Scouts bonus experience. Natural Wonders also give an adjacency bonus to Holy Site Districts in which all adjacent tiles receive +2 Appeal.
Cliffs of Dover
It appears with Cliffs adjacent to water and provides a bonus of +3 Culture and +2 Gold.
Crater Lake
It appears as a Lake and provides a bonus of +1 Science and +4 faith.
Dead Sea
It appears as a Lake and provides +2 Faith and +2 Culture. Additionally Units heal completely if rest and heal for one turn adjacent to the Dead Sea.
Galapagos Island
It appears on Coastal Terrain and provides +2 Science to each adjacent Tile.
The Great Barrier Reef
The Reef provides a bonus of +3 Food and +2 Science.
Mount Kilimanjaro
It appears as a Mountain and provides a bonus of +2 Food to each adjacent Tile.
Mount Everest
It appears as a Mountain and provides a bonus of +1 Faith to each adjacent Tile. Additionally Missionaries, Inquisitors, and Apostles who move next to Mount Everest will ignore Hills movement cost for the rest of the game.
Pantanal
It appears as Marsh and provides +2 Food and +2 Culture.
Piopiotahi
Provides a bonus of +1 Culture and +1 Gold to each adjacent Tile.
Torres Del Paine
Doubles the bonus yield of each adjacent Tiles.
Tsingy De Bemaraha
Provides a bonus of +1 Culture and +1 Science to each adjacent Tile.
Yosemite
Provides a bonus of +1 Gold and +1 Science to each adjacent Tile.
Source
Natural wonders don't directly provide a boost to amenities/happiness as they did in Civ5. As Auditore notes the immediate effect is an experience boost to the scout.
Natural wonders are also important if you are playing for Religous Victory because there is an Apostle promotion called Pilgrim that gives 3 extra spreads once the Apostle stands next to the natural wonder for the first time. It can be hard to find them on the map when you need to do this, but the trick is to use Strategic View, where the Natural Wonder will look exactly as in the icons Auditore posted!
Natural Wonders also come into play for at least one Great Person. Charles Darwin (Great Scientist) has a bonus that grants 500 science for each adjacent natural wonder. There are some natural wonders that extend over many tiles so you can multiply that by 6 or 7.
Natural wonders are also one of the possible locations for a National Park (which is unlocked by Conservation and provides extra tourism and amenities). National Parks must be designated on squares which are mountains, natural wonders, or have an appeal of charming or better. I don't think you have to be able to move a unit onto the square to do this given that mountains also count, so I don't think you need to worry if you can't walk on top of the natural wonder (need to confirm).
In summary, Natural Wonders don't play one specific role in the game, but they come into play for lots of specific situations. I'm sure there are many situations beyond just the three I mentioned here.
I am not sure if they also increase appeal for neighborhoods or not, but in any case that factor would already be set.