The Villa Gallimontana is a historical building in the first century AD. It was first established as a paramilitary organization by Emperor Augusto to maintain the order of Urber. Later, the so-called Hilariana Cathedral was established here. This is a religious complex that was abandoned until the 16th century and was acquired by the Mattei family to build an elegant residence in the Renaissance style.
This hidden gem of a park is on the Celian hill, next to the Colosseum (no, not the Palatine hill; the one across from it). With umbrella pines, fountains, 16th-century villa (during the Renaissance, the area was the property of the noble Mattei family), and ancient Egyptian obelisk, it's the perfect Roman escape from the busy nearby attractions. On the weekends, expect to see local families picnicking and relaxing.
In the San Giovanni neighborhood, this is a wonderful place to hear jazz in the summer. You sit under the beautifully lit pines and listen to great or only good music while having dinner or cocktails...it does get packed, but with good reason. It was definitely one of my favorite places when I lived in Rome.