You get to the gallery from the Main menu simply by choosing the option. A loading screen will appear then and after a while you find yourself inside the gallery.
The gallery changes the further you get into the game. That keeps it always interesting and makes it a great feature of the game!
The Gallery itself is a sort of temple consisting of 8 rooms connected by one circular chamber. Above each entrance you will find a significant symbol to help you guide through the rooms.
Here's a guide to each symbol:
First Picture:
Left symbol: A seahorse, the entrance leads to the "Island of Tranquility Image Gallery"!
Middle symbol: A lyre, go inside here for the "Soundtrack Archive"
Right symbol: A gearwheel, the "Man's Nightmare Image Gallery" is located here!
Second Picture:
Left symbol: A film projector, leads you to the "Film Gallery"
Middle symbol: Two bubbles, they get you to the "Dolphin's Nightmare Image Gallery"
Right symbol: Two heads, there is the "Credits Room"
Third Picture:
Left symbol: An alien head, here's the "Domain of the Foe Image Gallery"
Right symbol: An arrow, go inside this tube and you will get back to the Main Menu!
The gallery changes as you progress in the game. Image galleries will only open if you've reached the world already. Otherwise the room will be locked by a gate. It is similar with the Film Gallery. Films are only unlocked if you've reached it in the game as well. Only the Soundtrack Archive and the Credits Room can be entered and fully used from the beginning.
The image galleries contain 5 - 9 conceptual art pieces which are attached to the walls. A picture appears once you've collected all vitalits in a stage. So each picture represents a stage and is in most cases also thematically related to it. By singing at a picture you can focus and zoom in to it!
In addition there are a couple of secrets and nifty things to play with. We'll get to that later!