It's from the Akkadian version of Ištar's Descent to the Underworld; specifically a Neo-Assyrian manuscript from the library of Aššurbanipal, the last of the great Assyrian kings (ruled 668—627 BCE). I'm reading the text for a class in Akkadian this semester and I've been putting up the transcription and translation as I go (previous pieces of myth here, here, here, and here). If I have the time tomorrow, there will be more.

I'm glad you like!