This achievement is part of the main story as you need to fill the Knowledge Sequence before commencing with the final questline.
The Knowledge Sequence is divided into three parts with some of the locations throughout Atlantis being locked until you reach a certain level of the Knowledge Sequence. The Knowledge Sequence should be easily filled working through the quests across Atlantis and looking for the Keeper's Insights. I would advise to follow the quests first and then look for the Keeper's Insights (as one of them needs the first level of the Sequence filled).
You can gain progress through the completion of quests (+20 progress), finding the Keeper's Insights (+30), Isu Data Caches (+10) and Isu Data Codices (+3).
I found an interactive map for all Data Cache and Data Codices locations here:
https://mapgenie.io/assassins-creed-odyssey/maps/atlantis