Using "the" in this context is restricting our attention to a certain set of buildings, etc. In this context, it's probably clear which buildings are referred to. Let's say somewhere previously, he had just arrived in Paris and that arrival is the subject of discussion. While the reader is thinking about Paris, you can say "he walked across the numerous bridges." The reader knows which bridges these are, at least generally. Writing it this way focuses the reader's attention on the nature of the location.
Omitting the article indicates that the reader, and perhaps the writer, doesn't know which bridges and pavilions were crossed and they are mentioned only to show that the subject traveled a long way.