This is the 15270th most frequent Russian word.
посещаемых
"Visited" or "popular/frequented" (depending on context).
In this sentence, 'посещаемых' is used as an adjective in the genitive plural form that describes 'мест', indicating these places are often visited by people.
Это одно из самых посещаемых мест в городе.
This is one of the most visited places in the city.
Here, 'посещаемых' functions as an adjective modifying 'сайтов', suggesting these websites are frequently accessed.
Мы должны составить список самых посещаемых сайтов.
We need to make a list of the most visited websites.
In this context, 'посещаемыми' acts as an instrumental plural form adjective describing 'музеями', referring to museums that attract visits.