Alright, lets talk a moment about the nature of ORO.
I am a bitterly logical individual, and I'm currently embroiled in medical training. This is coloring my outlook, so I want to explain some things and then see what the consensus is.
There are two ways I see to make ORO.
The first is the one I'm currently doing and it's the "World turtle" design. Ie, the captured lands reside mostly on ORO's back, a vast mound of structures, towns, landmarks and natural formations piled onto and assimilated into the demonic machine that is ORO. The body of oro is mechanical, demonic and impossibly large, but it has a defined set up. It has a circulatory system in the form of a branching and complex train network. It has a mouth that eats cities, stomachs to digest them, immune system to protect itself, respiratory system to pump air to furnaces and such. And the demons within are either working for it or living inside of it as an environment. Or are symbiotic. In the case of this set up, you'd be spending your time mostly dealing with the captured lands and, once you reach a good spot or get something you need, you would mount an assault in and try to cripple an organ. You would do this until the entire beast is terminal and the heart shows itself.
The second would be one that is a lot more...well a lot less organized. I would relax that logical part of my mind that yells "Well, how does it walk?" and just say "it walks because its fucking demon magic, fuck you. Insert its magic I don't have to explain shit image here. In this case Oro would not be a bunch of lands riding a demonic engine. It would be an impossible amalgam of cities, villages, landmarks and natural features that is oozing across the world like a hellish katamari.
In the first case, the player experience would be one of being a tiny insignificant being atop a giant creature, shadow of the colossus but where the colossus is 25 miles in diameter and occasionally stops to eat cities before it continues to trudge onward. You would be acting as a cancer or a virus, infecting, taking over, striking at the organs and trying to bring it down.
In the second case it would be like walking into a neon urban nightmare, dreamlike, hellish, filled with impossible space and Penrose stairs. Trains exist but might go nowhere, or might not go to the same stations each time. An elevator you find in an open field might lead to an inverted cathedral where you walk among upside down gargoyles on the roof and try not to fall into the sky. The heart here would be buried deep in layers of contradiction and paradox, and would be reached by the forcible stabilizing element of our civilizations, which would act as islands of sense in an otherwise eldritch and inscrutable world.
Which of these sounds more interesting?
I should point out also that the first one will take longer to do because I have to get all the parts together, and it will necessarily be somewhat more restricted in what I make. The second one is much easier because I can just let my imagination run wild and create whatever bizarre, hellish, urban hatescapes I can think up at 3am while staring at the street lights. But it might feel more like a massive maze or dungeon compared to crawling through the guts of a mechanical elder god.
It's a hard choice.