flaw in floorboards

This is a popular question! Look at the map of the attic - there's a very thin, vertical strip at one point. The loose floorboard is located there. You'll get not one, but two keys. Can't say they're not generous, hmm?

That is correct, it's actually a small part of the wall that breaks open when you're in the right spot. Look for the short, narrow section of the main part of the attic. It should be an overhead shot when you're in the right section. The wall you can open is going to be on your left when you're on that screen. Also, I believe you can listen for a hollow sound when you step over the floor there.

Finding a specific screenshot of that particular area is going to be extremely difficult, but I'll try. In the meantime, here are some more directions:

ATTIC AREA

1. Open the locked door with the Rusty Key you got from the portrait.

2. Exit through the east door and be careful of Photosauri (plant creatures).

3. You'll be in a small hallway. Exit through the next door.

4. Head north and listen for the hollow sound when you pass through a narrow walkway. Use the crowbar on the tiny wall to your left and get two keys.