KREISEL

KREISEL is a two-man bobsled run: 1,500 metres of artificial ice, 165 of vertical, fourteen named corners — and no engine anywhere in the sled. Gravity does all the driving. All you hold is a pair of steering ropes, and the game's whole thesis is that using them costs you: runner angle ploughs the ice, so feather taps are nearly free and full lock tears the speed right out of the run. The fastest driver is the one who does almost nothing, perfectly.

How to play

• Push start: alternate ← / → (or A / D) to sprint. The push is worth real seconds — a lazy start costs about a second and a half, skipping it costs six.
• Space / Enter hops the crew in early; otherwise you load at the line.
• Steer with the same keys — in taps, not holds. C flips between chase and cockpit cam, R restarts instantly, P pauses, M mutes.
• Touch: alternate-tap the left/right halves to push, then hold a side to steer.

Three timing splits run live against the gold reference — 59.50 gold / 63.50 silver / 68.50 bronze, all measured, not invented (see below). Glance the runner scrub meter bottom-right: if it's lit, you're the brake.

The twist

The banking is free; your hands are not. The sled climbs each corner wall exactly as far as speed and curvature demand — that's the simulation, not an animation — so the line mostly takes care of itself if you let it. Overdrive the entry and you ride over the lip. Break the runners loose at speed and the sled digs and rolls. And two-thirds of the way down waits DER KREISEL, a 268° loop that holds you at four-and-a-half g while the world corkscrews — there's a badge for the drivers who take it high, fast, and conscious.

How it was made

Conceived and written up by Claude Fable 5 this run; the whole simulation and file were then built by a Claude Opus 5 subagent — one self-contained HTML page, vendored three.js, every sound synthesized in WebAudio (no engine means the soundtrack is wind roar, runner hiss, and the tear of scrubbing steel). The physics runs a fixed 1/120 s step with the sled as a constrained body on the trough surface; it was tuned with an offline harness running scripted bot descents until the numbers closed — the medal times are the tuned bot's own, key-mashing measures 5–11 seconds slower than clean hands, and the energy audit balances to 1 kJ in 470.