Sliding block puzzle

How to play the Gridlock Protocol

You are looking down on a strongroom floor. Steel rails, timber crates and fixed bolts are jammed across a grid, and in the middle sits the red payload, a crate with a glowing brass keyhole plate. The vault door is in the far wall. Slide the freight out of the way, clear a lane, and the payload rolls out through the door by itself. There is no submit and no timer.

• Rails (long steel boxes, two or three cells) slide only along their length.
• Crates (one cell, banded timber) slide in any of four directions.
• Bolts never move. Plan around them.
• A move is one piece sliding in one straight line, any distance. A long slide is still one move.

Par, undo and perfect par

Every hold shows its par: the fewest moves that can possibly solve it, proven by a solver that searches every arrangement. Clear it in par moves and you earn the PERFECT PAR stamp. Undo is free and unlimited, and Reset takes two taps, so par is something to chase, not a penalty. Once you clear a hold you can replay it from the start and keep your better result. Your streak counts the first clear.

Tips for sliding block puzzles

• Work backwards from the door. Look at the piece blocking the payload's lane, then at whatever blocks that piece.
• Check each rail's direction before you plan around it. A rail pointing the wrong way can never leave a lane that runs along it.
• Count free cells. You usually need to open space in two or three places before the key slide becomes possible.
• Prefer one long slide to several short ones. Distance is free, moves are not.
• Experiment. Undo takes back one move and drops the counter, so a bad idea costs you nothing.
• Stuck? The hints light the lane in cyan on the floor and frame the next piece to move.

A worked example. Say the payload sits on the bottom row, facing a door on the right, with an upright two-cell rail in its way. That rail can only slide up or down, so the question is which way it has room. If a crate sits above it and the cells below are free, slide it down and the lane opens. If a bolt pins it from below, the crate above has to move first, and now you have found your first two moves by thinking from the door back.

What makes our sliding puzzle different

This is our own game with our own rules: a brass and steel strongroom, not a car park. Pieces drag with weight, tick a rail click at every cell and stop at an obstacle with a knock. Let go and they glide to the nearest cell and land with a thud. The exit can sit on any wall, so you will not learn one layout and repeat it. When the payload reaches the door the bolts clack, the door swings open on its hinge and teal light floods the floor. It works on touch, mouse and keyboard, has a flat 2D fallback for older devices, and every hold is solved by a computer before it goes live.

A new hold at your midnight

Each player gets the hold for their own local date. One spare key covers a single missed day. The share card shows your moves against par and never the route you took.