The hull

Behind the meadow is a dark layer a few metres thick. It holds the world together, stores its energy and makes its gravity. The inside of the world has the anime look. The hull is dark and grainy, lit only by light that leaks through from the meadow and by the droids' lamps.

Three of these four Midjourney pictures were edited in Paper, two to fit the story and the physics and one to make it more dramatic. Each edit can switch back to its original. They run from the outside in.

From outside

A black sphere in grey-green space with one lit square hatch on its curve; a tiny craft dives in toward it from the upper left, trailing a thin streak of thruster light. — **d2-1** · edited in Paper

This is a black sphere about 200 m across, with one lit hatch and a small craft coming in toward it. The hatch is the world's only door.

In the original the craft hangs still beside the sphere. The edits have it dive in toward the hatch from high on the left with a thin trail of thruster light, or skim low over the skin with its lamp lighting the black surface.

The sphere is black because the skin keeps almost all the light that lands on it, about 41 MW at Earth's distance from the Sun. That energy runs the Lantern and has to leave as heat, so a black ball at that distance warms to about 5 °C, where it gives off as much heat as it takes in, and glows only in the infrared, near 10 µm. To the eye it is the darkest thing in its sky.

The window

Looking up from inside a dark structure at a huge round window full of stars, with a row of thin struts below. — **c3-3** · unedited

This is the one window in the skin, seen from inside the hull above the struts that hold it. The world doesn't turn, so the stars stand still. It is the only place where you can see out, and nobody on the meadow can see it, because the ground is in the way.

Under the meadow

In near darkness, a curved row of still ribs with thin lines of pale light between them; a small droid holds on in an alcove of the dark wall. — **c2-1** · edited in Paper

These are the ribs that carry the meadow, seen from below, with daylight leaking through the seams between them. A droid holds on in an alcove of the outer wall.

In the original the ribs are smeared sideways, because the prompts described a spinning hull like those in NASA's 1975 settlement study, so the edit makes them stand still.

Down here there is no weight, because the ground's compression exactly cancels the tension in the air above it (see Making gravity). The droids move by holding on, clipping to rails and pushing off.

A panel lifted out

From the dark hull, a round opening framed by trusses shows the far meadow of the inside world with paths and tiny figures; below it hangs a large dark sphere above a row of silhouetted machines. — **c6-3** · edited in Paper

Here a meadow panel has been lifted out, seen from the hull. Through the hole is the far meadow, 196 m away across the hollow. That ground faces the centre, so from here it looks like an aerial view, with paths and players.

The original shows blue sky and cumulus clouds. Cumulus clouds need kilometres of rising air, and this world is 196 m across, so the edit replaces them with the far meadow.

What the dark sphere is hasn't been decided. One idea is a spare Lantern, kept unlit in the hull.

What the hull is

It doesn't spin. Ours has skin gravity, which the hull holds as a layer of tension (Making gravity): the pull is the same everywhere on the ground and fades with height. Spin at this size would mean 4.5 turns a minute, weightless poles, and a sideways push of 43% of your weight when you run at 10 m/s, so nothing in these pictures turns.
It keeps spare ground. Half a sphere's worth of charged panels lies folded against the outer skin. They unfold when the world morphs, so any shape up to 1.5 times the sphere's ground area keeps the meadow's 22 m/s² (Any shape).
From outside, it has weight. The outer skin carries half the compression that balances the tension, and the world's mass is its energy divided by c², about 4.7×10¹⁵ kg with the spare ground. Standing on the outer skin you'd feel about 32 m/s², more than the meadow's 22.
It shares the meadow's air. The black outer skin holds the atmosphere, so a panel can be lifted without losing any air. At this size, about 4 cm of steel holds one atmosphere with a factor of two to spare.
It lights the inside through the Lantern. Spread over the 120,700 m² of meadow, 41 MW is about 340 W/m², roughly a third of noon sunlight on Earth.
It was charged by its builders. The field's tension, the frame that holds it and the spare ground store about 4.2×10³² J, as much as the Sun puts out in about 13 days. Building one world takes a yard five centuries, drawing about 1/14,000 of the Sun's output (Building a world).