Can I open the starred or alternate-path doors on my first run?

Steps

1. Treat every star door you meet on the first playthrough as scenery and keep going; the walkthrough says one exists in every new area and none is required for the main story.
2. Finish the story once. Steam lists a single story-completion achievement, Charlotte's Hero — Scale the entire tower, from start to stunning finish.
3. Start the tower again in the replay mode. Steam names it in Adventure Plus Antic — Dive into the tower again with Adventure Plus!
4. On that run the star doors give an alternative route through the main story rather than a bonus room, which is how the walkthrough describes their purpose.
5. Clearing that second run is its own achievement, Plus Mode Pandemonium — Beat the Tower one more time!
6. If you are chasing secrets, cross-check the two community checklists on our Secret Safari page first; they label some areas as Adventure Plus entries and disagree on two of them.

Requirements / limits

• No developer text names the star door specifically. The identification of star doors as the Adventure Plus route doors comes from the walkthrough's wording, with Steam's achievement list supplying the mode's official name and the reviews confirming the mode's behaviour.
• That finishing the story is what unlocks the mode is stated on camera by one player at the end of one narrated run, on a build predating the 19-21 August updates. It is the only source held that observes the transition itself, and it is a single account.
• The two community secret checklists disagree about whether Kids Corner and West Poolrooms belong to the first run or to Adventure Plus.
• Steam's Secret Safari achievement asks for every hidden secret area in a single playthrough, which does not sit comfortably with checklists that split entries across two runs. That tension is unresolved.
• A patch that changes the replay mode or the door rules would invalidate this answer.

Common mistakes

• Hunting for a key, switch or code to open a star door during the first playthrough.
• Treating star doors as optional secret rooms rather than alternate story routes.
• Assuming the published checklists have settled which run each secret area belongs to.
• Assuming that finishing the story unlocks the doors inside the same save without starting the replay mode.

What the 23 August transcript sweep added

The unlock condition on this page was assembled rather than observed: the achievement list names the mode, a walkthrough describes doors that open on a second run, and two reviews describe a post-clear mode. Nobody in those sources is present at the moment of unlocking.

A narrated full playthrough transcribed on 23 August reaches the ending, and immediately after the credits sequence the player states that completing the game also unlocks Adventure Plus. That is one person's account on one build and is not treated as more than that. It is worth adding because it is the only source held that observes the transition itself rather than describing the mode from either side of it.

Still unverified

• Does every star door open in Adventure Plus, including the early Hotel one?Single source onlyThe walkthrough states the rule for star doors as a class and names the Hotel one as an example. No developer source confirms door by door, so a single restricted door in a later area would not surprise us.
• Can the Secret Safari achievement be completed in one playthrough if some areas are Adventure Plus only?Not verifiedThe achievement text says a single playthrough, but both community checklists tag some entries as Adventure Plus. Nobody has published a resolution.