This quest is one of the Limited World Quests that the Midsummer Island Adventure event offers in the Golden Apple Archipelago. The quest pertains to the fog surrounding the island and the time to break through the heavy fog. It surprisingly offers not one or two chests, but three Precious chests at the end including the 40 Primogems, 300 Adventure Rank EXP, and 20,000 Mora.
Teleport to Twinning Isle and glide down south of it to the hole. You have to break the pile of rubble to get to the conch and journal. Use elemental sight if you need to.
You start the quest after reading a journal on the table near the conch down the hole of the Twinning Isle.
After reading the journal, the quest will direct you to sail north at a specific time: 10:00 am. You can use the wind currents as a guide through the whirlpools and rocks.
Afterward, you will arrive at a Nameless Isle. It also has two common chests sitting on top of the rock formation. Once you climb to the top you’ll see three Precious Chests and another mural for the Limited World Quest: The Other Side of Isle and Sea next to the chests. Observe the mural to complete the quest to get the quest rewards.