Dwarf/Gnome Door (5e Environment)
From D&D Wiki
A Dwarvern or Gnomish door is a magical door that is completely hidden from view to all those who don't already know it exists. Locating a Door requires a successful Arcana or Perception check of 25. Gnomes and Dwarves get Advantage to these checks. Passive Perception cannot locate the door.
Any creature with True-Vision sees the door as a normal door. Dispel Magic, See Invisibility, or Anti-Magic Field all expose the door. Non-detection is permanently cast on the Door. The creator of the door can set a particular time or event or password to make the door reveal itself automatically.
Revealing the door doesn't necessarily open it.