I can put a city of civilians beyond his power to find. One of them.

How big a city?

The actual constraint is how big the surrounding land for agriculture. A city of any size would be fine.

How much land, then?

Ten square miles, if a good location for it can be found.

Does it have to be near the ocean?

That doesn't seem wise at all; mountain ranges are harder for the Enemy to have his servants explore manually foot-by-foot, which is the only way it could be found.

Any other constraints I should know about?

The more the house of Fëanor has to do with a plan, the worse its odds of success.

Oh, is that why the Enemy is still alive. Can I get around this in some way?

The Enemy is still alive because sheer energy cannot kill us. The Enemy turned this to his benefit because his attackers were doomed. They could get around it by surrendering their claim to the authority to rule and not taking a role in planning. They are not very likely to do this.

I will plan on a non-planet-destroying option. I don't suppose we made enough of a dent in him that you and the rest of the Valar can just finish the job?

We could.

I can petition my brethren.

That would be great. I have a next step but it's entirely possible it will not cooperate with me. If you're worried about wrecking Beleriand I am happy to make another pass of evacuations. Does the other side of the cylinder have atmosphere?

The world is flat.

I heard it was flat on top and otherwise a cylinder; was my information mistaken? ...Are you not allowed to describe it in front of the Elf or something?

I suppose it's technically a cylinder but a very very narrow one; flat is a much better approximation. There is atmosphere on the other side.

Would it be appreciably more difficult for Morgoth to get there?

Yes. But it's not lit and not particularly habitable.

The sun doesn't go around -? Okay, not worth the detour then.

It does but it doesn't maintain a trajectory convenient for life below.