One of the many puzzles within Elden Ring relates to the Stargazers’ Ruins. It involves a Jellyfish and being rewarded with the Primal Glintstone Blade and Fancy Spin gesture.
Here is how to complete it…
SPIRIT JELLYFISH ASHES
In order to begin this puzzle you will need to have completed the Roderika side quest, during the side quest you should be given the Spirit Jellyfish Ashes.
If you have yet to get the Spirit Jellyfish Ashes, return to the Roundhold Table and speak with Roderika again and make sure to exhaust her dialogue.
Now with the Spirit Jellyfish Ashes in hand make your way to the Stargazers’ Ruins, you can get here by teleporting to Snow Valley Ruins Overlook over in the Mountaintops of the Giants.
At Snow Valley Ruins Overlook continue down the hill and across the bridge on the left. Once across continue to the left and you will arrive at the Stargazers’ Ruins.
Once at the Stargazers’ Ruins you should come across a Jellyfish and over hear a voice calling out for their sister. The cries are actually coming from the Jellyfish here.
In order to solve the Jellyfish problem you will have to summon the Jellyfish, who is actually the sister, Aurelia.
NOTE: You will not actually lose the Jellyfish summon. Merely summon it and it will still be accessible.
After solving the Jellyfish issue a nearby seal will then be broken. This seal is actually just down the nearby stairs here.
So head down these stairs, leading underground. You will now come across a treasure chest containing the Primal Glintstone Blade
(Primal Glintstone Blade reduces FP that is consumed when using spells. However, maximum HP is reduced)