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< Beneath the surface, Crypt or Castle?
"The Ruins of Forgotten Castle" is the name of the wider area in which the Howling Crypts and Inferno(?) maps are located - you can see this in the map selection screen. The outdoors Ruins map which is not currently available is also located there.
So yeah, you can definitely complete the Beneath the Surface quest. I finished it probably a couple weeks ago.