Noble Chateaus
Concept · Stellaris 4.5.2
Noble Chateaus in the Stellaris encyclopedia: Each Noble Chateaus grants +2 Stability in the Overlord's capital.
Noble Chateaus in the game's words
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Each Noble Chateaus grants +2 
Stability in the Overlord's capital.
A home away from home, this is the perfect place for the Overlord's ruling elite to let off steam, so that they don't cause incidents back home.
Source: common/game_concepts (concept_noble_vacation_homes) and localisation/english, Stellaris Cygnus v4.5.2 (9776).