The Missing Crystalline Cores puzzle is part of the Like Rhyme and Song, Summer Reverie quest. It requires you to look for the missing cores and solve puzzles to get them.
Find the missing crystalline core 3 | Genshin Impact
As you currently go through Like Rhyme and Song, the Summer Reverie quest, you will eventually come across a section where you have to search for missing Crystalline Cores. Fortunately, it's not too difficult to find them since their locations are already marked on the map.
The only problem is that you have to solve some puzzles to get them. In this guide I will tell you what you need to do to solve the puzzles.
The quest will give you Persikov's Manuscript which contains all the information you need to solve the puzzle. You can find it in your inventory so you can check it from time to time. If you look at the manuscript, you will find red arrows pointing to three islands. This is where you can find the missing crystalline cores.
