The "underground" aspect

[fountainhead]

I'm a fan of the Zork series, and though I've played the original, Return to Zork and Zork Nemesis, I've never actually played one all the way through (I remember exactly where I left off in the monastery in Zork Nemesis in 1998 and still plan to finish it one of these days, lol). Anyway, one aspect of the lore has always confused me. The setting for the games is always referred to as the "Underground" Empire.

Now, does this mean this world is in our "real life", present day universe and is simply hidden underground so no one ever sees it, a la Harry Potter? Or does the whole thing take place in a separate game universe from our own and within that universe, the adventurer stumbles upon the Underground Empire? I'm leaning towards the latter, because taking place in a separate, magical universe would explain how the Empire has a "sky" even though it's supposed to be underground.

[KM3K]

I agree. It's the latter. You can learn more about the world of Zork in the Zork Compendium.