This The Last of Us 2 Walkthrough for Chapter 6: Seattle Day 1 – The Aquarium is a heartfelt flashback that has 0 collectibles. Focus on the story for this one.
The Aquarium Walkthrough
The Aquarium opens with a cutscene and you’ll need to jump into the water. Follow Owen up the stairs and lift the door together. Check out the boat. You can even slide down the railings in the stands here.
Head to the next door and head up and over to get into the next area. In the main area, you’ll find a note by the mural. It doesn’t count as an artifact though.
Max’s Place is locked but you can go upstairs and find a note held by the corpse, it’s not an artifact either. Fortunately, you can get a key to enter Max’s Place.
Return and go to open Max’s Place. Follow Owen onto the ladder in the elevator shaft. A cutscene will play and lead into the next area: Seattle Day 1 – Hostile Territory.
Source: IGN.com The Last of Us 2 Walkthrough Chapter 6: Seattle Day 1 – The Aquarium