What are Noita's secrets?

Noita’s progress screen tracks which perks the player has obtained, which spells the player has used, and which enemies the players has defeated by showing a little icon with the name and description. At the top of the progress screen, however, is a more enigmatic tracker, counting the number of secrets the player has discovered. For example, in my own game:

The game doesn’t specify which secrets are unlocked though, only showing one vague description (in my case "Discovered the secret below").

What does Noita recognize as a secret, and what is the wording for each of them?