Space

Space is the layer above the surface, and the first thing you notice is the gravity. You jump higher and you fall slower, roughly the way a featherfall effect behaves, and it stays on the whole time you are up there. The sky goes black with stars visible even at noon. Nothing generates in space naturally. The only solid ground is whatever a Floating Island or a Living Tree pushes up into it, so almost everything you stand on up there is something you built.

For all the visual language of being in orbit, there is no penalty for the height. No Suffocation debuff, no breath meter, no damage over time. Whatever you build up there is exactly as safe to stand on as ground level, and the only thing that will hurt you is what spawns on it.

Space and the surface do not have a clean dividing line. Different features switch on at different heights, and those heights are set as fractions of the vertical distance from the surface line up to the world ceiling, which generation randomizes. An absolute depth reading that puts you in space in one world will fall short in the next. If you want the real numbers for the world you are in, fly to the very top until your head touches the border, read the Depth Meter there, and work down from that figure.

Fallen Stars spawn in space, and they will land inside anything you have built at altitude, which quietly turns a long skybridge into a star farm you do not have to attend. Harpies are the permanent residents, joined by Wyverns in hardmode. Martian Probes are more likely to appear here than anywhere else, so sitting high up is the quickest way to trigger a Martian Madness once you are eligible for one. Ordinary surface enemies like slimes and zombies will also spawn in space if you give them somewhere to stand, which is a decent argument for keeping skybridge platforms narrow.

Until hardmode begins, nothing native to space will spawn in the middle ten percent of the world by width. A small world is 4200 tiles across, so that is a 420 tile band, and the exclusion reaches 210 tiles either side of dead center. If you want an early sky base without fighting harpies the whole time you are hammering platforms in, build it directly above the middle of the map. The protection ends the moment hardmode does.

• A pillar of blocks or Rope. Cheapest option, and the only one that also gives you a controlled way back down.
• Wings, Rocket Boots or any jump accessory, launched from a Floating Island or another tall structure rather than from the ground.
• An Ice Rod, which both builds you a step and resets wing flight time the moment you touch the block.
• A Gravitation Potion or a Gravity Globe, flipping gravity so you fall upward instead.
• A minecart track laid on a long rising slope.
• A flying mount, which is the easy answer once you have one.
• Ghost form after a hardcore death, which will get you there but will not award the Into Orbit achievement.

Two smaller notes for anyone setting up shop. Space needs to be pure for the space-exclusive fishing catches, and the Forest Pylon works up here, which matters because space has no pylon of its own.