The massive structure standing at the southeast end of the Circus Maximus serves as the headquarters of the United Nations Food and Agriculture Organization (FAO). This building plays a major role in global efforts to fight hunger and promote sustainable agriculture.
The rooftop of the FAO offers what many consider the most impressive views across Rome. Visitors can see sweeping panoramas of the city’s historic landscape, with monuments and ancient sites stretching out in every direction. However, access is tightly controlled. Entry to the roof is limited to those who have permission or personal connections with someone working inside, due to strict security measures.
Source - https://en.wikipedia.org/wiki/FAO_Headquarters