It is highly recommended to join a guided tour! Because the Retiro Park covers a large area, the various attractions are a bit scattered. Unless you plan to save money (the park itself does not require tickets) and are willing to spend more than half a day walking around, it will be more efficient and enjoyable to have a professional guide to assist us. Our tour guide was very dedicated to explaining the history of Spain to us and guiding us to various attractions in the park (he even took the trouble to take us to the places we wanted to visit). It was a wonderful experience!