Plovdiv of which are high. Because of these hills, Plovdiv is often referred to in Bulgaria as "The City of the Seven Hills". Plovdiv is host to a huge variety of cultural events such as the International Fair Plovdiv, the international theatrical festival "A stage on a crossroad", the TV festival "The golden chest", and many more novel festivals, such as Night/Plovdiv in September, Kapana Fest, and Opera Open. There are many preserved ruins such as the ancient Plovdiv Roman theatre, a Roman odeon, a Roman aqueduct, the Plovdiv Roman Stadium, the archaeological complex Eirene, and others. The oldest American educational
Plovdiv Airport and a tie-up between Hainan and Plovdiv Airport Invest. On 28 March 2018, Bulgarian Government awarded the consortium of HNA Group and Plovdiv Airport Invest a 35-year-long concession on Plovdiv airport in return for investments reaching €79 million, including a new cargo and passenger terminal. On 19 of July the consortium of HNA Group and Plovdiv Airport Invest have declared that it won't sign the concession contract which opens the road for the classified on the second place to take the concession. On the west side of the airport is located 24th Helicopter Air Base of the Bulgarian Air Force,