Portal: Walkthrough & Tips

A complete guide to Valve's 2007 puzzle classic: how portals and momentum work, a chamber-by-chamber outline, the GLaDOS fight, every achievement, and getting it running well today.

Researched September 2026 — current as of the Steam build (last patched June 27, 2025; Portal with RTX free DLC released December 8, 2022). Live games change; check the linked sources if something differs.

Quick Start

Two portals, one rule: Anything that goes into one portal comes out of the other, keeping its speed. "Speedy thing goes in, speedy thing comes out."
Portals only go on flat, light-colored concrete-style panels. Metal, dark, or grated surfaces reject them.
Look for somewhere to drop from. Most momentum puzzles are solved by putting a portal on the floor under a long drop.
You start with a one-portal gun. You only control the blue portal until the fully powered device (the Lab Rat achievement).
There's no fall damage. The Long Fall Boots let you land from any height. Water and energy pellets still kill you, and so do turrets.
Cubes solve most buttons. The Weighted Storage Cube (and one very special Companion Cube) hold down large floor buttons.
Look for the Rat Man's dens. Scrawled messages behind the walls ("the cake is a lie") are part of the story. Portal into the gaps to find them.
It's short. A first playthrough takes roughly 3–4 hours. The replay value is in the advanced chambers and challenges.

Controls (PC default)

Action	Key
Fire blue portal	Left mouse
Fire orange portal	Right mouse
Use / pick up / drop	E
Jump	Space
Crouch	Ctrl
Move	WASD
Quick save / quick load	F6 / F9

Quick-save before tricky flings. It's the fastest way to retry.

Core Mechanics

Flinging (momentum)

The key technique: fall a long way into a floor portal and you shoot out of the other portal, placed on a wall, at the same speed. You'll often place the exit portal mid-fall, so shoot it while you're already dropping.

Fall into the floor portal from higher up to fly farther.
Aim the exit portal on an angled surface for an upward arc.
Air control is limited. Line up your approach before you commit.

Hazards and objects

Thing	Behavior
Energy pellet (high-energy ball)	Bounces off surfaces and kills on contact. Route it with portals into its receptacle to power platforms or doors.
Weighted Storage Cube	Holds down buttons, blocks turret fire, and can be carried through portals.
Turrets	Friendly-sounding but deadly. Knock them over from behind, drop cubes on them, or portal under them.
Emancipation Grill	The shimmering field that removes your portals and vaporizes objects carried through it.
Toxic water / goo	Instant death.
Security cameras	You can grab them off the wall (Camera Shy achievement).

Chamber Walkthrough Outline

The main game runs Test Chambers 00–19, then an escape through Aperture's backstage areas and the final fight.

Chambers	What you learn
00–01	Buttons and cubes. Pre-placed portals demonstrate how they work.
02–03	You get the portal gun (blue only). Place portals to get past walls.
04–05	Carry cubes through portals and drop them onto buttons.
06–09	Energy pellets. Redirect them into receptacles, ride the moving platforms, and put portals to more creative uses.
10	Flinging, the core momentum technique. Also the best place for Terminal Velocity and Long Jump.
11	You get the fully powered portal gun (orange portal) and the Lab Rat achievement.
12–13	Puzzles that use both portals: buttons plus momentum.
14–16	Longer puzzles with pellets, platforms, and turret gauntlets. Chamber 16 is a turret-heavy "live fire" course.
17	The Weighted Companion Cube. Carry it through the whole chamber, then "euthanize" it in the incinerator to continue (Fratricide).
18	The longest test chamber. Big flings, pellets, and turrets.
19	The finale test. Ride the platform, then escape the "party" before the incinerator (Partygoer).
Escape	Aperture's maintenance areas: Rat Man dens, turret ambushes, and rocket turrets.
GLaDOS	The final chamber.

Stuck-point tips

Chamber 10: Put a portal on the floor at the bottom of a big drop and the exit on the far wall, then jump in from the highest ledge.
Chamber 16: Portal behind turrets to knock them over, or carry a cube as a shield.
Chamber 18: Take it room by room. Most sections combine a fling with redirecting a pellet. Look for flat portal-able panels high up.
Chamber 19 escape: When the platform nears the fire pit, look for a portal-able wall on the side, place both portals, and walk out.

The GLaDOS fight

GLaDOS drops a personality core (the Morality core first). Pick it up and throw it into the incinerator.
The rocket turret fires homing rockets at you. Put one portal in its path and the other facing GLaDOS so the rocket hits her.
Each rocket hit knocks another core loose: the Curiosity, Intelligence, and Anger cores. Incinerate each one.
Keep moving between rockets. Neurotoxin is on a timer, so don't waste time.
After the last core the game ends. Stay through the credits for "Still Alive".

Achievements (15)

Achievement	How to get it
Lab Rat	Acquire the fully powered portal device (story, chamber 11).
Fratricide	"Do whatever it takes to survive": incinerate the Companion Cube (story, chamber 17).
Partygoer	"Make the correct party escort submission position decision": escape the incinerator at the end of chamber 19 (story).
Heartbreaker	Complete Portal.
Friendly Fire	Knock down a turret with another turret. Carry one turret into another.
Long Jump	Jump 300 feet in one fling. Chamber 10's big flings work well.
Terminal Velocity	Fall 30,000 feet total in one go. Place portals on the floor and ceiling directly above each other and fall in a loop (chamber 10 works).
Camera Shy	Detach security cameras from the walls. Grab them with Use.
Cupcake / Fruitcake / Vanilla Crazy Cake	Beat 2 / 4 / all 6 advanced maps.
Basic Science / Rocket Science / Aperture Science	Bronze / silver / gold medals on all challenges.
Transmission Received	Find the hidden radios in the test chambers and carry each one to the spot where it picks up a signal. Its Steam description is just "..?", and only about 4% of players have it. Use a radio-location guide.

Advanced maps and challenges

Beating the game unlocks advanced versions of chambers 13–18 (harder layouts) and challenges on those same chambers:

Least Portals: Solve it with as few portals as possible. Plan where every portal goes before you shoot.
Least Steps: Minimize footsteps. Momentum and flings cover distance without walking.
Least Time: Speed runs. Plan routes and practice them.

Gold medals take real routing. Community videos show the intended solutions for gold.

Running Portal Today

Steam Deck / controllers: Plays well with a controller; check the Steam store page for the current Deck compatibility rating.
Linux: Native. Valve shipped a run of fixes in 2025: a Linux startup crash (February), the Linux executable-stack error (May 19), a particle crash, a reworked main-menu layout for all resolutions and clipped credits ASCII art (May 28), and fire effects in mods (June 27).
Portal with RTX: A free DLC (December 2022) with full ray tracing and remastered textures, made with NVIDIA. It needs a ray-tracing-capable GPU and is demanding.
Mods: Portal: Prelude is a well-known fan-made prequel built on Portal. The sequel, Portal 2, is where most modern community content lives.

Achievement rarity (Steam global stats)

The challenge medals are the hardest: Basic Science, Rocket Science, and Aperture Science each sit around 3% of players. Camera Shy (about 4%) and Transmission Received (about 4%) are next, because both are easy to miss without a guide. If you're hunting 100%, grab Camera Shy and the radios on your first run so you don't have to replay chambers.

Replaying a chamber

The main menu's chapter select lets you restart from any chapter you've reached. That's the fastest way to go back for missed radios, Long Jump, Terminal Velocity, or Camera Shy without replaying the whole game.

Common Mistakes to Avoid

Placing portals on non-portal surfaces. If a shot fizzles, the surface is wrong. Look for the pale panels.
Not falling far enough. A weak fling usually just needs a higher drop.
Carrying a cube through an Emancipation Grill. It's vaporized, and you'll need the dispenser for a new one.
Standing in turret sightlines. Turrets have a short wind-up. Break line of sight or carry cover.
Skipping the Rat Man dens. They're the best part of the story's subtext.

Advanced Tips

Fire the exit portal mid-air. Most flings require it. Practice in chamber 10.
Use portals to "move" pellets. Shoot a portal where the pellet will hit so it re-exits toward the receptacle.
Shooting portals through portals works. Look through one to aim at a surface beyond it.
Quick-save before every fling when you're going for challenges.
Least Steps: Every footstep counts, so let momentum carry you wherever possible.

FAQ

How long is Portal? About 3–4 hours for a first playthrough, and much less once you know the solutions.

Is Portal with RTX free? Yes, if you own Portal on Steam. It's a separate free DLC that needs an RTX-class GPU.

How do I get Transmission Received? Find the hidden radios in the test chambers and carry each one to a specific spot where it picks up a signal. You need a location guide.

How do I get Terminal Velocity? Put portals directly above each other on the floor and ceiling and fall through the loop until you've fallen 30,000 feet.

What's the "cake is a lie"? A message scrawled by the Rat Man (Doug Rattmann) in the hidden dens. It refers to GLaDOS's promise of cake.

Is Portal worth playing before Portal 2? Yes. It's short, sets up GLaDOS and Aperture, and Portal 2 builds on it directly.