Lintel Portal Puzzle

The old works were built around doorways that open onto each other. A fitter with a two-ended portal device walks them room by room, from the chalk pits to the night yard, using nothing but height, speed and where the doors are put.

Open two linked portals and fall into one to fly out of the other at the same speed. 35 hand-made rooms with crates, belts, water, light and moving walls.

Walk and jump through side-view rooms to reach the lit door. Your device opens two linked portals, a ring and a diamond, on pale chalk surfaces only; dark slate, grates and doors do not hold them. Anything that enters one portal leaves the other at once, keeping its speed and turning to face the way the exit points, so falling into a floor portal shoots you out of a wall portal sideways and a floor portal sends you back up as high as you fell. Grates stop bodies but let shots, light and water through. Crates press buttons that open doors, belts carry what stands on them, water turns wheels, lamps light sensors, blocks slide on their tracks, and in the last chapter a cart carries one of the portals. After a fast pass time runs slower for a moment: open the next portal mid-flight to chain passes. Every room has a spark to take and a par for the number of portals you open.