Number 1 is ok.
Number 2 - Try These monuments are visited throughout the year.
Number 3 - Try In 2004, the Forum of the Cultures will take place.. I don't really understand what you were trying to say here, so my answer might be wrong too.
Number 4 - Try It was founded in the X century
(sorry it has taken so long to reply - I've no idea why, but our forum did not show this message until now)
Student or Learner