Complex sentence: The second largest Serbian city of Novi Sad is sometimes known as "Serbian Athens", while the Fruška Gora and Ovčar-Kablar gorge near Čačak, the site of 17 (12) Serbian medieval orthodox monasteries is called the "Serbian Athos".
Split into simpler sentences: The second largest Serbian city of Novi Sad is sometimes known as "Serbian Athens". The mountain of Fruška Gora is the site of 17 monasteries and is called the "Serbian Athos".