The Cleft of Five Worlds

From the introduction: The Cleft is a massive sinkhole, reaching from mountainous heights into the lower world. Here, the Seree built one of their most ambitious engineering projects, a Lycaeum that drew aspirants from the entire empire. Only the Seree knew its location in the overworld, but as a powerful ley nexus, the Cleft has a way of being found along many strange pathways. Before the Seree were scoured from the world by the gods, the Cleft was the meeting place of five cultures - not all of them allies. Now, the wizards are gone, but the Cleft rumbles on in the shadow of their works.