Secret doors are a special type of sticker found in Paper Mario: Sticker Star. They are located exclusively at Outlook Point and sell for 80 coins. Their main purpose is to be Paperized onto silhouettes of doors found mainly on walls to see what is behind, usually several powerful stickers or a Thing. They can also be used in battle to successfully escape by having a door appear and have Mario walk through. However, in special occasions (such as when fighting Bowser), the door may collapse and fall on Mario, making him unable to escape.
A secret door is only found outside of Outlook Point twice; in Ice Flow after Mario reveals several Hidden Blocks, and in Bowser's Snow Fort after Mario defeats or pays the two Shy Guys holding the Traveling Toad hostage.
Secret door locations
* - A Secret door sticker can be found in the level.