This is the 546th most frequent Finnish word.
tunnettu
Known; famous.
Here, 'tunnettu' is describing Helsinki as being 'well-known' for its significance or recognition.
Helsinki on tunnettu kaupunki Suomessa.
Helsinki is a well-known city in Finland.
In this case, 'tunnettu' characterizes the subject, the artist, as being 'renowned' or 'famous' in their field.
Hän on tunnettu taiteilija useissa maissa.
He/She is a well-known artist in many countries.
Here, 'tunnettu' expresses the quality that makes the event stand out, emphasizing its reputation for a particular attribute.