The Travel Journal is part of two quests in One Way Heroics: Plus and even constitutes it's own ending. It can only be filled out by a Tourist class, which has significantly reduced stats.
"The One Chasing the Travel Journal" Edit
In One Way Heroics: Plus, after unlocking the Force Knight and the Ninja, the player can take on the Quest for the Travel Journal. This quest involves a series of three periodic interrupt events replacing the usual Demon Lord interruptions, where the player finds fragments of the journal but is ambushed at every site containing a part of the Journal.
After the final boss fight, the player finds the full Travel Journal but discovers that many of the pages are blank, and upon this discovery, the Tourist class is unlocked.
Filling the Travel Journal Edit
The Travel Journal is a special side-quest and victory condition only available when playing the Tourist. The player is allowed to make an entry once per day, and based upon how exciting the situation is will decide how many pages are filled. In order to get this ending, the player must fill 1,000 pages.
Info on completion mechanics is available on the Tourist page under The Travel Journal section.