Climbing the stair the giants left standing…
No ads on the stair — just one button, eight stones, and a chained moon
Play Ossa: The Giants' Stair — a free Greek-myth stacking runner
Climb the stair the giants stacked to heaven. Spend your stones to clear rubble and chasms, duck the low sky-gates and cut Artemis free. A free one-button stacking runner: 30 chapters, four acts, endless mode.
Ossa: The Giants' Stair is a free browser-based stacking runner built on Greek myth. In the myths, the twin giants Otus and Ephialtes — the Aloadae, sons of Poseidon — piled Mount Ossa on Olympus and Mount Pelion on Ossa to make a stair to heaven, then carried off Artemis, goddess of the moon and the hunt. Our story starts the night the moon went out. You are Aethon, a mason's son from the Vale of Tempe. The temple where you cut stone for the goddess is dark, her hunters are scattered, and the giants' stair is still standing. So you climb it, one carried stone at a time.
The loop is one button and two numbers. Leap to cross rubble and chasms; height decides what you can cross and what you cannot. A rubble wall of three stones costs three stones to clear, a chasm two wide costs two, and every stone you spend is gone — you rebuild the stair by catching marble shards that float along the ridge. Then the giants' low sky-gates arrive, and they kill the obvious strategy: a stair taller than the gate's clearance is stopped dead. The game is not about getting tall. It is about arriving at each obstacle at exactly the height it asks for.
How to play
- Leap with one button. Press Space, ↑ or W, click the stage, or tap anywhere on a phone. You are airborne for 0.46 seconds; rubble, gate and chasm checks happen the moment your body reaches them.
- Read the ring. A gold ring closes on your climber. Leap when it lands on the inner ring: too early and you land in front of the wall, too late and you are still rising when your chest meets it.
- Pay in stones. Rubble costs its height in stones, a chasm costs its width. Land a perfect leap — inside the last fifth of the window — and you get one stone back plus a gold chime.
- Shed before gates. A sky-gate prints its clearance in stones. Press ↓ or S to drop one stone at a time; arrive taller than the lintel and the gate shears every stone above it.
- Charge the moon. Moon fragments fill the silver bar. Spend it on Artemis' Aim: the world drops to 55 percent speed for two and a half seconds.
- Outrun the storm. Three stumbles and the storm at your back takes you. Reach the summit gate with none and the chapter is worth three stars.
Controls
| Input | Action |
|---|---|
| Space ↑ W · click · tap | Leap. Vaults rubble and bridges chasms if your stair is tall enough |
| ↓ or S | Shed one stone — the only way to fit under a low sky-gate |
| Shift or E | Artemis' Aim — slow the world while the silver bar drains |
| Esc or P | Pause |
| R | Restart the chapter |
| M | Mute the synthesised score |
The rules, exactly
| Thing | What it does | What it costs |
|---|---|---|
| Marble shard | Adds one stone under your feet, up to eight | Nothing — but high shards need height to reach |
| Rubble wall | Must be leapt, and your stair must be at least as tall as the wall | Its height in stones |
| Chasm | Must be leapt late; the stair is dropped in as a bridge | Its width in stones |
| Sky-gate | Passes only if your stair is shorter than the printed clearance | Every stone above the lintel, plus a stagger |
| Moon fragment | Fills one third of the Aim bar and scores 250 | Nothing |
| Perfect leap | Ring inside the last fifth of the window | Refunds one stone, scores 150 |
| Stumble | Crash or fall; 0.85 seconds of recovery | One of three. The third ends the climb |
| The storm | Follows you the whole way up; every stumble brings it closer | Ends the run at three |
How it differs from other endless runners
| Ossa | One-button jumpers | Stacking towers | |
|---|---|---|---|
| What you manage | Height as a currency: earn it, spend it, shed it | Timing only | Accuracy only |
| Failure | Wrong height for the obstacle, not a missed tap | A missed tap | A misaligned drop |
| Level design | 30 authored chapters with a measured stone budget | Endless procedural | Endless procedural |
| Ending | Chapter XXX: the chain is cut | None | None |
The four acts of the stair
| Act | Chapters | Where you are | What changes |
|---|---|---|---|
| I · The Vale of Tempe | 1–8 | Dawn in Thessaly, the foot of the stair | Rubble only; the ring teaches itself |
| II · Ossa's Shoulder | 9–16 | The first mountain's spine, storm gathering | Sky-gates appear; height becomes a liability |
| III · Pelion's Spine | 17–24 | Broken ridge, night, wind through the gaps | Chasms, gusts, tighter spacing |
| IV · The Iron Sky | 25–30 | Above the weather, under a chained moon | Darkness, double walls, gates in sequence |
Why every chapter can be finished
Every chapter is generated against a stone budget and then run by a bot. The generator only places a rubble wall or a chasm if the stones it costs are already in your hands, and it plants shards to refill the stair before the next wall. After that, a reference bot plays the chapter with the same physics the player gets — same jump arc, same collision rules, same stumbles — and has to reach the summit gate with zero stumbles. The verification suite also measures the tightest leap window in every chapter; measured across all thirty it is 221 milliseconds, and nothing ships under 180.
Strategy that actually works
- Travel light into gates. If a gate reads 4, you want two or three stones, not seven. Clear the wall before it, then shed the change.
- Bank stones before a gap. A chasm is a bill, not a jump. Arriving with one stone at a two-wide gap is a fall, however clean your leap.
- Jump late over gaps. Rubble wants an early leap; a chasm wants the last moment, so the stair lands on the far lip instead of inside it.
- Hunt high shards when the next gate is high. Shards that float at head height are only reachable with two or more stones.
- Save Aim for the dark. In Act IV you cannot read the next obstacle until the ring appears. Half speed is worth more than a chapter of reflexes.
Technical notes
Everything is generated: no image is loaded, no audio file is played, no third-party script runs. The mountains, the storm, the marble and the stair are Canvas 2D drawn from the same level data the reference bot uses, and the wind, the stone clack, the chime and the low drone are synthesised with the Web Audio API. The rules contain no random numbers — every shard, wall and gate comes from a seeded generator, so a chapter plays identically on every device. Progress and stars live in your own browser under ossa.stair.v1. Nothing is uploaded, because there is no server.
JustPlays Original — handcrafted, ad-free · Browse all free action games →
Ossa: The Giants' Stair — frequently asked questions
What is Ossa: The Giants' Stair?
It is a free browser runner built on Greek myth. In the myths, the twin giants Otus and Ephialtes stacked Mount Ossa on Olympus and Mount Pelion on Ossa to make a stair to heaven, then carried off Artemis. Our story begins the night the moon went out: you are Aethon, a mason's son, climbing their stair with a chisel and a rope to cut the chain. Thirty chapters, four acts and an endless ninth heaven, played with one button.
How do you play with one button?
Your runner climbs the giants' stair on his own. Press Space, the up arrow, W, or tap anywhere to leap. Leap over rubble and chasms: each one costs the stones you are carrying, so a tall stair clears tall walls, but a low sky-gate will take your head off. Collect marble shards to rebuild the stair, gather moon fragments to charge Artemis' Aim, and reach the summit gate before the storm catches you.
Why does height help and hurt at the same time?
Height is the whole game. Rubble walls and chasms are cleared by spending stones equal to their height or width, so a taller stair crosses more. But the giants built low gates as well, and a stair taller than a gate's clearance is stopped dead: you lose every stone above the lintel and one of your three chances. The art is arriving at each gate at the right height, not the maximum height.
How do the stars work?
Three stars for reaching the summit gate without a single stumble, two for one stumble and one for any finish. Perfect leaps, moon fragments and unspent stones add to your score, and the score is kept per chapter. A stumble is any crash into rubble, a fall into a chasm or a collision with a gate; three stumbles and the storm takes you.
Is every chapter actually beatable?
Yes, and it is measured rather than promised. Each chapter is generated against a stone budget, then a reference bot runs the whole chapter with the same physics the player gets: all thirty chapters and the first three waves of the endless mode are cleared with zero stumbles before a build ships. No chapter ships with a leap window under 180 milliseconds, and that number is printed by the verification suite, not guessed.
What is Artemis' Aim?
Moon fragments charge a single power: hold Shift or E, or press the moon button on a phone, to slow the world to just over half speed for two and a half seconds. It does not make you invincible. It buys the half second you need to read a gate, a double wall or a gap in the dark of the fourth act.
Does it work on a phone, and does it cost anything?
No download, no install, no account and no payment. The whole game is one HTML5 page with no external assets: the mountains, the storm, the stair and every sound are drawn or synthesised in the browser. Progress and stars are stored in your own browser, it runs down to a 320-pixel screen in portrait or landscape, and the single-button control works with a keyboard, a mouse or a thumb.