Diablo 4 Kurast Undercity explained

What is the Kurast Undercity in Diablo 4? There are many ways to acquire both levels and loot in Diablo 4 - getting through the campaign should see you net plenty of both, but once that's over with, the real test of the endgame begins. Having an experience focused on helping you get stronger, while also being fun, is exactly what the Kurast Undercity is there for.
The Diablo 4 DLC brings with it a ton of new content that should appeal to veterans and newcomers alike - the Spiritborn class alone is worth the price of entry. There are plenty of new ways to interact with the world: the Realmwalker world event, the Dark Citadel, and, of course, the Kurast Undercity.
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