This is the 7723rd most frequent Russian word.
знаменитые
"Famous."
Here, 'знаменитых' is an adjective in its plural form and is used to describe the noun 'космонавтах' (cosmonauts). It indicates that the cosmonauts being discussed are famous.
Она читала книгу о знаменитых космонавтах.
She was reading a book about famous cosmonauts.
'знаменитыми' acts as the instrumental plural form of the same adjective and describes 'достопримечательностями' (landmarks), communicating their well-known status.
Этот город известен своими знаменитыми достопримечательностями.
This city is known for its famous landmarks.
In this sentence, 'знаменитые' stands in its plural nominative form, modifying 'личности' (personalities) to express their renown.