Castle Wall is a free online loop logic puzzle. Draw a single closed wall through the centres of the squares, moving up, down, left or right, never branching or crossing itself. The clue squares tell you where it goes. A white square must end up inside the wall and a black square outside it, and the wall never passes through either. Some clue squares also carry a number and an arrow: the number is how many squares' worth of wall run in that direction along the clue's own row or column, counting every segment that points the same way as the arrow. Drag from square to square to build the wall, drag back to rub it out, and tap a square to cross it out when you know the wall misses it. A clue the wall already breaks turns red. Every board is built by the game itself, has exactly one answer, and is proved solvable by deduction alone before you see it. Eight levels grow from a 6×6 courtyard to a 10×10 citadel. No download, no account.
How to play Castle Wall
- Draw one closed wall: a single loop through the centres of squares, moving up, down, left or right. It may not branch, cross itself or touch itself, and it does not have to visit every square.
- Clue squares are never on the wall. A white clue square must end up inside the loop, and a black clue square outside it.
- A clue with a number and an arrow counts the wall that runs in the arrow's direction along its own row or column: the total length of those segments, one for each step from square to square. Wall crossing the row at right angles does not count, and squares beyond another clue still do.
- Drag from square to square to draw the wall; drag back over a stretch to rub it out. On a keyboard, arrow keys move the cursor and Shift with an arrow draws or rubs out one step.
- Tap a square (or press Space, or right-click) to cross it out as a reminder that the wall misses it. A crossed-out square takes no wall; tap it again to clear the cross.
- A square where the wall branches is ringed in red, and a clue turns red once the wall breaks it — too much wall in its direction, or, when the loop is closed, a wrong count or the wrong side.
- The board is solved the moment the wall is one closed loop that keeps every clue. Undo steps back one change, Clear wipes the board, and New Puzzle deals another board on the same level.
- The ? button fixes one step of the wall: a wrong line is rubbed out first, otherwise it adds a line of the answer, next to your own lines where it can. Three per board.
Tips
- Start with the zeros. An arrow with 0 means no wall runs that way along its line, so every square in that direction is either missed by the wall or crossed by it straight across the line, never along it.
- A number as big as the line it looks along is the same gift the other way round: every step that way carries wall.
- A white clue square and a black one never touch, not even corner to corner. When they sit two apart in a row or column, the square between them is on the wall, and the wall runs straight through it across that line.
- Every white square is inside the same single loop, so the wall has to reach round all of them at once. A black square between two whites forces the wall to bend in and around it.
- The outside is one piece that reaches the edge of the board. A black square boxed in by the wall would be a hole in the castle, which one loop cannot make.
- Cross out the squares you know the wall misses: it stops a drag from wandering through them by accident.
- On the last three levels, try a stretch of wall in your head. If following it through breaks a clue or traps a black square inside, that stretch is wrong.
FAQ
Is Castle Wall free to play?
Yes. It runs in the browser with no download, no sign-up and nothing to buy. All eight levels are included and unlock as you solve them, and New Puzzle deals more boards on any level you have reached.
What are the rules of Castle Wall?
Draw one closed loop through the centres of some squares, moving orthogonally, without branches or crossings. Clue squares are never on the loop: white ones must be inside it and black ones outside it. A number with an arrow gives the total length of the loop segments in that direction along the clue's row or column.
What exactly does the number on an arrow count?
Walk from the clue in the arrow's direction to the edge of the board and count every step from one square to the next that the wall makes along that same line. A wall that crosses your path at right angles does not count — only segments running the same way as the arrow. Another way to see it: count the square borders the wall crosses on that line.
Who invented Castle Wall?
GM Puzzles credits the style to puzzle designer Palmer Mebane, and it has since appeared in puzzle championships. The puzzles here are generated by this game.
Does every puzzle have exactly one answer?
Yes, and it is checked rather than assumed. Each board is built from a real loop, and clues are taken away only while a program that makes forced moves alone can still finish it; a board it can finish that way has only one answer. The tests confirm it with an exhaustive search as well.
Will I ever have to guess?
No. A board only ships if it can be finished by deduction. On levels 1 to 3 every step is direct: a clue square's own side, an arrow that has all its wall or needs all that is left, or a square that cannot reach the rest of the inside. Levels 4 and 5 each need at least one bottleneck — a square the inside or the outside has to pass through to stay in one piece. Levels 6 to 8 each need "what if" steps: one to four on level 6, three to eight on level 7, and five or more on the 10×10.
Why does the wall not go through every square?
Unlike Yajilin, where the loop must visit every free square, Castle Wall only asks for one closed loop that keeps the clues; most boards leave several plain squares outside the wall or inside the castle. Crossing those squares out as you find them is the quickest way to keep track.
How many levels are there?
Eight, from a 6×6 board to a 10×10. Each level's boards are built fresh with a seed, so Replay gives the same board again and New Puzzle a different one at the same difficulty.
Does Castle Wall work on a phone?
Yes. Drag with a finger to draw the wall and tap to cross a square out. On a phone held upright the board fills the screen's width; held sideways, the buttons move beside it.