This is the 13083rd most frequent Spanish word.
poseer
To possess or to own.
Here, 'poseo' is used to indicate ownership of a specific item, showing possessive meaning.
Poseo un libro antiguo que mi abuelo me regaló.
I own an old book that my grandfather gave me.
In this sentence, 'poseer' is employed to denote possessing an abstract quality or ability.
Ella parece poseer un talento extraordinario para la música.
She seems to posses an extraordinary talent for music.
Here, 'poseer' is used to indicate that possession of something (the treasure) is attributed to the castle in a mythical context.