The Unity Fountain is a golden statue of a human and an elf holding hands, located in the center of Atlantis. It symbolizes the unity between humans and elves and was built when humans lived in Atlantis, but it is also ironically the entrance to the pathway to Nightfall. It may be torn down and replaced with a statue of Linh, Sophie, and Keefe in the future, although it is not completely certain yet.
Though it might seem like the first time, Nightfall was not the first time that the Unity Fountain was mentioned - in fact, It was a part of a memory in Prentice's mind in Book 2: Exile
↑"There was a fountain in the center of it all, two golden figures standing in a round pool, holding hands as colored streams of water showered them from every direction. A shadow of a girl appeared between them and took off through buildings, shattering everything she touched before she dove into a sea of shards." ~ page 240, hardcover