World

Terraria keeps your character and your world in two different files and neither owns the other. Any character can walk into any world, with one exception: Journey characters and Journey worlds are sealed off from everything else in both directions. Everything stored on the character travels with them, which includes the inventory, the Piggy Bank, the Safe, the Defender's Forge and the Void Vault. Those containers are character storage, not world storage, and they are what makes moving material between worlds workable at all. A chest you placed stays where you placed it.

Four decisions are permanent: size, difficulty, which evil biome the world gets, and the seed. The evil biome is the one people underestimate. Corruption and Crimson are not reskins. They give different ore, a different boss, different accessories and different weapons across most of pre-Hardmode. To get both sets in one playthrough you either make a second world and carry material across, or you run a seed where both generate. Shimmer will swap some counterpart items over once you can reach it, but not all of them.

The small tree next to each world is a progress readout, not decoration. Its left half is drawn as that world's evil biome and its right half stays a plain Forest tree. Once the world enters Hardmode, part of the icon turns Hallow yellow. Kill the Moon Lord and it gains a gold border, which is the only completion mark the game gives you. Worlds running special seeds get their own icons, and one with several enabled cycles between them.

The same screen is where you copy a seed, rename a world (the file on disk keeps its original name), favorite it so it sits at the top and cannot be deleted by accident, or move it to cloud storage.

You arrive at 8:15 AM at the world spawn, near the horizontal center of the map. That point never moves. Your personal spawn does: place a Bed inside valid housing and set it, and every return item sends you there instead. Magic Mirror, Ice Mirror, Recall Potion, Cell Phone and Shellphone all land on the same tile. The Potion of Return is the one worth stacking, because it leaves a portal at the spot you left and lets you go straight back to it.

A world has two states and killing the Wall of Flesh moves it permanently from the first to the second. The Hallow and a fresh band of evil biome are cut through the map, spawn tables change everywhere, and nothing reverses any of it. If a world is your building project, think before you take that fight in it. Keeping a second world purely for progression, and leaving the nice one in pre-Hardmode until you actually want the new content, is a normal way to play rather than a strange one.

Do not quit straight after the kill, either. Leave before the message about the ancient spirits appears and the game still has to generate the new biomes, so it will hold you on a loading screen while it finishes.

The world remembers progression. The characters do not share it. A fresh character joining a Hardmode world meets enemies that kill on contact, and someone who skipped the mechanical bosses cannot help with what comes after them. In a group the practical answer is one shared world that everyone plays in together, rather than everyone hosting their own and drifting apart in gear.

World names are generated from a small grammar of adjectives, places and nouns, capped at 27 characters. That cap has one casualty. One of the nouns in the pool, the Greatest Generation, is unreachable: even the shortest name template already runs past 27 characters once you attach it. There is also a one in ten thousand roll for 'The Constant'.

Each world is a single file with a .wld extension. On Windows they sit under Documents, My Games, Terraria, Worlds, unless you moved them to Steam Cloud, in which case they live in your Steam userdata folder instead. Back that folder up somewhere. A corrupted save has no in-game recovery.