Go to the River Height Path, drain the water and jump under the bridge. “Papirize” now. You can see a red panel for a sticker. Now you have to stick on any sticker you want. There will be a ?-Block. Jump against an you will get the sticker in a better version. After that you can leave the level and repeat it.
If there is no space in your “Sticker Album”, you can do two things:
To go the Museum, rescue the green Toad which was crushed by the Papercity. You only have to “papirize” the fountain.
Hier sind ein paar Tipps für Geheimtüren