There are two hidden stages in the new Arknights event Twilight of Wolumonde: TW-S-1 and TW-S-2. You may unlock them upon finishing four of the puzzles in Antique Diary (refer image above).
Here are the answers on the puzzles:
Mission 1 – Don’t let your enemies touch the Gramophone in TW-4
Basically, spawn camp.
Mission 2 – Don’t rely on Gramophone in TW-6
In another words, don’t deploy operators on the tiles that charges the Gramophone aka spawn camp.
Mission 3 – Farm TW-7 until you killed 20 Mudrock Colossus
Those rock giants, if you’re wondering.
Mission 4 – Use only 6 units in TW-8
Mission 5 – Complete TW-S-1 Tribulation