walkthrough (Fatal Frame: Maiden of Black Water)

and then stuck on the "sixth drop" - "Find a way to open the hatch."

In short, you rush into the ephemeral sanctuary on the 1st floor, an altar with a coffin. You kill a ghost. You approach the coffin, interact with it, they tell you that there is a hatch under it and you cannot open it BUT the camera reacts to something, take a photo of this coffin. 3 pictures appear. 1 photo ghost in the room with coffins. 2 photo ghost in the boat. 3 photo ghost behind bars, on the same floor where the boat is a corridor with a lattice window. You return to the room where you wanted to open this box.