In order to start the quest, you need to have at least 1 Stone of Remembrance. You get this by leveling up your Statue of the Seven - Geo tower. However, in order to complete the quest, you need the tower at max level and have all 9 stones.
In order to reach max level, you need to collect all the Geoculus in Liyue region, then offer them all to the tower. After reaching max level, you will get the achievement "Unmovable Mountain".
Climb up the glowing pillars that's in Cuijue Slope, and insert the stones into the square that looks like a face. Inserting the first one will give you the quest details. You also get a treasure chest for every stone that you insert.
It helps that you mark the ones that you already inserted in order to not lose track. Otherwise, you can see the difference between the lit pillars and the ones that aren't.
After inserting all 9 stones, the main entrance to the ruin will open.
Inside the ruin, there will be 1 Ruin Guard, a couple of Geovishap Hatchlings, and finally a Ruin Hunter. There will be times when the enemies are enveloped in an elemental aura, which will reduce their damage taken. You need to destroy the rocks that shows up to dispel the barrier to make the fight easier.
Once you defeat all the enemies, the treasure room will be open. Pick up all the rewards to continue with the quest.
You will also get 1 guaranteed 5 star Royal Flora, which is a flower piece of the Noblesse Oblige artifact set. The substats of the artifact are random though.
After picking up the quest item inside the ruin, the quest will mark 2 npc locations in Liyue Harbor. You are able to exchange the key item only to one of them, so make sure you choose carefully before deciding it.
Exchange Option 1
The first option is to talk to the npc that's right beside the stairs, next to Mingxing Jewelry, which is marked in the map with a diamond icon. She only appears in this location at night, around 9 pm. She will offer you 200,000 Mora if you give it to her.
If you are not able to see her in the stall next to the stairs, she will be by the docks, just north of the Liyue Harbor teleport waypoint.
Exchange Option 2
The second option is to give it to Bolai. He will offer you 180,000 Mora, and 5 Adeptus' Temptation.
This dish is not exclusive to this event, since you can make it yourself once you get the recipe. It's also not the "delicious" version that you get when you time the cook perfectly. However, the ingredients to make 1 can be a hassle to get, so trading it for 5 of the dish is a pretty good option.