CelSector Walkthrough: All Six Sectors in Order
A sector-by-sector CelSector walkthrough order, with the keycard, chest and point-of-no-return notes that matter before you drop into the next area.
Quick answer: CelSector runs six sectors in a fixed order: A1 and A2 in the prison and labs, B1 and B2 in the sewers and the hive, then C1 and C2 in the deepest facility. You cannot choose the order and you cannot backtrack through a closed door, so the safe route is always the same: clear the side branch before you take the main door, then move on.
That structure is simple, but it hides the two things that actually cost runs: keycards that sit behind a one-way drop, and weapon pickups placed just before a ledge you cannot climb back up. This page gives you the order and the rules; each sector page has the room-by-room route.
Stage select keeps your keycards but resets doors and arenas. Sweep the side rooms before you take the exit.
What order do the CelSector sectors go in?
| Order | Sector | Setting | Main threat | What you leave with |
|---|---|---|---|---|
| 1 | A1 | Prison | Infected mutants, larvae | First keycard, SMG, three clothing chests |
| 2 | A2 | Laboratories | Dog packs, zombies | Shotgun and sniper (both easy to miss) |
| 3 | B1 | Sewers | Slime, earthworms, fast ants | Generator hub, save room, cosmetics |
| 4 | B2 | Alien hive | Spiders, wasps, queen wasp | Hive keycard, web-room cleanup |
| 5 | C1 | Deep facility | Light puzzle, slimes, jellyfish boss | Boss route, far-right keycard and chest |
| 6 | C2 | Final facility | Tentacles, final boss | Ending, gallery unlock |
The letters are not chapters in a menu; they are the three facility layers. A is the prison and its labs, B is the flooded infrastructure and the nest below it, and C is the control level where the escape route finally opens.
How the sector structure actually works
Each sector is a loop, not a corridor. You enter at one edge, the main door sits near the far side, and the side branch curls back to the entrance. That is why the game feels open without being a metroidvania: the branch gives you a keycard or a gun, then returns you to the room you started in.
Two consequences matter more than any single fight:
- Clear the branch first. If you take the main door, the game moves you forward and the branch closes. The stage-select screen lets you replay a sector, but it resets doors and arenas, so a missed chest means re-clearing the whole stage.
- Keycards persist, doors do not. A keycard you picked up stays collected when you replay a sector. A door you opened does not stay open. That is the reason a cleanup run feels different from a first run even when you are walking the same rooms.
There is no map screen worth relying on. The stage-select list is the closest thing to a progress tracker, and the clothing and gun lists are better completion checkers than the map.
The four rules that save a run
1. Never drop before you have swept the ledge. A2 is the worst offender: the first shotgun and the first sniper sit near a high platform, and the drop after it is one-way. If you jump down early, you finish the sector without either gun and have to replay it.
2. Treat every dark side room as a chest room. CelSector hides clothing in alcoves, not in glowing chests on the main path. If a room has a ladder, a broken railing or a ledge you can just reach, it usually has something.
3. Bank the save room before a boss door. Save rooms refill you and give you a clean outfit state. Walking into C1's boss with a shredded outfit is the most common avoidable death in the game.
4. Do not fight in open rooms with flyers. Wasps and jellyfish punish standing still. Pull them into a doorway, kill the grabbers first, and only then move.
Sector-by-sector route notes
A1 — Prison. The first keycard is behind a one-way drop into the larvae hall, and the SMG room has three clothing chests on its left side. The larva egg arena hands you the final keycard for the sector. Full route: A1 walkthrough→.
A2 — Laboratories. Dog packs come in waves, then a long zombie corridor. The shotgun and sniper are before the high drop; after it, the final door is close. Full route: A2 walkthrough→.
B1 — Sewers. Three generators light the hub and open the save room. The start ledge alone holds four cosmetic pieces, and the elevator is the exit. Full route: B1 walkthrough→.
B2 — Alien hive. Spider webs slow you, wasps swarm in threes, and the queen wasp is the first real boss check. The hive keycard is past the web corridor. Full route: B2 walkthrough→.
C1 — Deep facility. The red/green light puzzle gates the next room, slimes fill the parkour stretch, and the boss spawns flying jellyfish. After the boss, the tentacle corridor hides a keycard and a chest at its far right end. Full route: C1 walkthrough→.
C2 — Final facility. A yellow-lit corridor, one last save room, then the two-headed final boss. The fight is an ammo management problem more than a damage check. Full route and boss plan: C2 and final boss→.
What is actually missable in CelSector?
Guns and clothing are the only categories that can be permanently missed in a run. Keycards persist and achievements are account-wide, so a missed keycard costs time, not completion. The missable list is short:
- A1: the three clothing chests around the SMG room and the maggot pit.
- A2: the shotgun and the sniper before the one-way drop.
- B1: the four cosmetic pieces on the starting ledge.
- C1: the keycard and chest at the far right end of the tentacle corridor after the boss.
If you are already past one of these, finish the run and use stage select. The secrets and chests guide→ lists the cleanup order so you do not replay the same sector twice.
FAQ
How long is CelSector? Six sectors, with A and B taking the bulk of the time. A straight run is a long evening; a completion run adds a second pass through the stages for chests and guns.
Can you backtrack between sectors? No. Once the sector exit loads, the previous area is closed until you replay it from stage select.
Do I need to replay stages for the ending? No. The ending only requires the final boss. Replays are for clothing, guns, capacity and the gallery.
Is there a true final boss or a secret ending? There is one ending and one final boss. The post-game adds a gallery, a sandbox room and cheats, not a second story path. See the ending and post-game guide→.
Sources
Official source: CelSector on Steam ↗ · CelSector demo on itch.io ↗ · Steam news and patch notes ↗