This page of the guide to The Witcher Monster Slayer contains a detailed description of the third quest in the game - A Joint Venture.
Rewards: 60 gold coins.
If you want to start the quest, you must examine the secret treasure map. You will find this map in your inventory and in the journal, in the quest description.
When you look at the map ,you will get a new access point. You must go to this location to continue the quest.
At your destination, you will find a stone monolith. Its four walls are covered with runes.
You must click them in the correct order:
This way you will be able to read the inscriptions.
An Offering for the Gargoyle King
Once you read the inscription on the obelisk, three points will appear on the map:
You only have to get one of the artifacts. Heart will be the correct choice.
Fighting the King
Go to the Gargoyle with the heart. This enemy's difficulty level is medium.
The Swift potion and Elemental Oil will work best in this fight.
Your treasure is an elven figurine. You must take it to a researcher who's interested in handmade items. This will start the next quest.