Assassin’s Creed Odyssey has many trophies and achievements you can unlock. To achieve 100% progress, you have to solve or unlock all these tasks.
In this guide we show you the following trophy/achievement:
Complete Markos’s questline.
You need to play the side quest "A Business Opportunity" to start Markos's questline, you will found it at the island "Kos" (sub-region "Highlands of Asklepiades").
It starts by finding Markos in a cage inside the enemy fort, where the quest marker is. You must free him and carry him back to his house to continue the questline.
If you are looking for a complete overview of all trophies and achievements or other puzzle solutions, here is our Assassin's Creed Odyssey 100% Walkthrough.