In a game full of monsters and treasures, maps are an essential tool to find your way in or find your way home. But maps often don't tell you what you really need to know, and that's when you need an extra little something to help reveal the important stuff the map doesn't show.
Wondrous item, rare
This small golden plaque is inscribed with tiny symbols around its edges, but the center of the cartouche itself is blank. Invented by treasure hunters and tomb robbers, once per day it can be placed next to any map, including one drawn by its owner, to reveal something hidden in the area that is not shown on the map, such as a secret door, hidden room, trap, or secret compartment inside a table, cabinet, throne, altar, or similar structure or object.
A map cartouche does not reveal creatures, but it can reveal hidden hazards, such as green slime or yellow mold. The map cartouche must be held next to the map for 1 full round to reveal the hidden feature. If multiple hidden features are present, the map cartouche reveals the nearest feature to its current location. Wisdom (Perception), Intelligence (Arcana), Intelligence (Investigation) and Dexterity checks with respect to the revealed hidden feature gain a +2 bonus, as do Armor Class and saving throws if the hidden feature makes an attack roll or forces a saving throw.