Bowser's diary

Bowser's Diary can be found in Paper Mario while playing as Peach after rescuing Star Spirit, Eldstar. The diary is found in the room that has the secret passage to Peach's Room, the diary says Mario must go to Dry Dry Ruins to save the next Star Spirit, Mamar.

Trivia
According to Bowser's Diary, these are the days in Mushroom Kingdom:
 * O/O
 * O/X
 * X/X