The Monument to the Unknown Hero, located on Avala Mountain on the outskirts of Belgrade, is a reminder of the mass casualties the Serbian people suffered during World War I. The identity of the hero has not been verified, though some documents claim that in the grave rests a 70-year-old Muslim man from the Pešter Highlands who was killed by an enemy grenade in 1915.

After members of the Allied Forces began building similar monuments, King Alexander I decided to construct a similar structure in Serbia. To make room for the Serbian monument, the medieval fortifications atop the hill were destroyed. 

The grave's architectural design resembles an ancient temple and includes a sarcophagus made of black granite. It's surrounded by caryatids representing the people of former Yugoslavia: Bosnian, Montenegrin, Dalmatian, Croatian, Slovenian, Vojvodina's, Serbian, and Old Serbian women. The inscription at the top of the sarcophagus reads, "Alexander I King of Yugoslavia to the Unknown Hero." The tomb with the remains of the unknown hero is located in the crypt, underneath the monument. 

The monument instantly caused some controversy, as people believed the unknown hero who fought and died for the Kingdom of Serbia was used to propagate an idea of a unified Kingdom of Yugoslavia. The area soon became a popular picnic area and a memorial complex. The architecture of monument gives a striking impression, especially observed during the morning mist, along with the nearby built hotel, decorated with depictions of mystical creatures of the forest and wilderness.