Walls in Trail: How Barriers Make the Path Easier to Find
Walls in path puzzles take away choices, and every lost choice is information. Corridors, forced turns, fences with gaps and a walled 5x5 solved step by step.
Walls make a path puzzle easier to read, because every wall takes away a choice. In Trail a wall sits between two squares, and the line cannot pass through it. That removes one exit from each of those squares. A square with only two exits left must use both, just like a corner. So walls create corridors the line must follow, turns it must take and fences it can only cross at a gap. Start every walled puzzle by counting exits next to the walls.
This guide is for Trail players moving up to Hard and Expert, the levels with walls, and for anyone playing LinkedIn's Zip, where some puzzles have walls too. If you are new to the rules, how to play Trail covers them first.
How walls work in Trail
In Trail you draw one line from 1 through every square, passing the numbers in order and ending on the highest number. The line moves up, down, left or right, never crosses itself, and cannot pass through thick walls. A wall is drawn along the side of a square, between it and its neighbour. It is not a square of its own: the squares on both sides of a wall still have to be visited, the line just cannot step directly from one to the other.
LinkedIn's Zip works the same way. Its rules, as GM Puzzles put them when Zip launched in March 2025, say the path cannot cross itself or any given walls, and some puzzles include walls while others have a fully open grid.
The diagrams in this guide draw walls as thick bars, just like the app:
To talk about squares, this guide uses R2C3 for row 2 (counted from the top), column 3 (counted from the left).
Count exits, not squares
Every wall lowers the exit count of two squares, and a square with two exits that is not the start or the end must use both. That is the rule that solves most walled boards. A square's exits are the neighbours the line could still step to: not across the board's edge, not through a wall, and not into a square that already has both of its links.
| Square | Exits with no walls | With one wall beside it | With two walls beside it |
|---|---|---|---|
| Middle of the board | 4 | 3 | 2: both links forced |
| Edge of the board | 3 | 2: both links forced | 1: must be an end |
| Corner | 2: both links forced | 1: must be an end | 0: impossible |
The middle column of that table is the useful one. An edge square with one wall beside it behaves like a corner. A middle square boxed in on two sides behaves like a corner too. So a few walls can give you as many forced links as all four corners of the board together.
The right-hand column has a quiet message. A square with only one exit can only be where the line starts or finishes. In Trail those squares are the 1 and the highest number, so in a well-made puzzle you will only ever see a one-exit square under one of those two numbers. If an empty square near a wall seems to have one exit, you have probably miscounted, or the line you have drawn has taken away an exit it should not have.
Corridors
A run of walls parallel to the edge of the board makes a corridor, one square wide, that the line must run straight through. Each square inside it has a wall on one side and the edge on the other, so it has two exits, both along the corridor.
Follow the exits square by square. R1C2, R1C3 and R1C4 each have a wall below and the edge above, so each must link to its left and right neighbours. That joins the whole top row into one straight piece. The corners R1C1 and R1C5 have two exits each, so the piece continues down into R2C1 at one end and R2C5 at the other. Six links, and no number in sight.
Corridors also form between walls and the line. Once part of the line runs alongside a wall, the squares between them are a corridor just the same. That is why it pays to recount exits beside every wall each time the line moves.
Forced turns
A wall at the end of a straight run forces the line to turn, and this is how walls steer the line around a board. Imagine the line running along row 3 towards a wall on the right side of R3C4. It cannot carry straight on into R3C5, so at R3C4 it must turn up or down.
Forced turns combine with exit counts. If R3C4 also has a wall along its bottom, it has only two exits left: up to R2C4 and left to R3C3. Both are links, and the turn is fixed before you have drawn any of it. The worked puzzle below starts with a square exactly like that.
The other side of a wall matters as much. R3C5, on the far side of that wall, has lost its left exit. If it is on the edge of the board, it is now down to two exits, up and down, and both are links. One wall, two forced squares.
Fences with a gap
A long line of walls with a single gap, a fence, can only be crossed once, and that tells you a lot about the whole route. Each crossing has to use the gap, and the line can only pass between two particular squares once. So the line crosses the fence exactly once. That means 1 is on one side and the last number is on the other, and the far side is covered in one unbroken pass.
Parity tightens this further. Colour the board like a chessboard, with the corners dark, and every step of the line changes colour. R2C5 is a light square. The top two rows hold ten squares, five of each colour, and the line covers them in one pass starting on that light square, so the tenth square, where the line ends, is dark. The last number in this puzzle can only be on R1C1, R1C3, R1C5, R2C2 or R2C4. A quick check by computer confirms it: with 1 at R5C1, a full line exists for each of those five end squares and for none of the other five.
With two gaps, the line can cross once or twice. If it crosses twice, out through one gap and back through the other, then 1 and the last number are on the same side and the far side is visited in one excursion. In general, an even number of crossings puts both ends on the same side and an odd number puts them on opposite sides. Path puzzle strategies explains parity in more detail.
A walled 5x5, solved step by step
This small puzzle shows walls standing in for numbers: it has only 1 and 2, and four walls. It is smaller than the app's walled levels, but every step is the kind you will use on them, and it has exactly one solution.
- Corners. R1C1, R5C1 and R5C5 are empty corners, so each uses both its neighbours: R1C2, R1C1, R2C1; R4C1, R5C1, R5C2; and R4C5, R5C5, R5C4. R1C5 holds 2, the end, so it needs only one link.
- Squares beside walls. R3C4 has walls on its right and bottom, so it links up to R2C4 and left to R3C3. R3C5 has a wall on its left and the edge on its right, so it links up to R2C5 and down to R4C5. R4C4 has walls above and to the right, so it links left to R4C3 and down to R5C4.
- The bottom row fills in. R5C4 now has both its links (R5C5 and R4C4), so R5C3 has only R5C2 and R4C3 left and links to both. That fills R4C3 and R5C2.
- The left side. R4C2 has lost R4C3 and R5C2, so it links to R3C2 and R4C1. R3C1 then has only R2C1 and R3C2 left, and links to both.
- Around the first wall. R2C2 has a wall below it and R2C1 is full, so it links to R1C2 and R2C3. R3C3 already links to R3C4; its only other free neighbour is R2C3, so they link.
- The two numbers. 1 at R1C3 has one free neighbour, R1C4, so the line starts there. R1C4 could link to 2, but that would end the line after three squares, so it links down to R2C4. Finally 2 takes its last free neighbour, R2C5.
Count the reasons: three corners, three squares beside walls, and then a chain of squares that had two exits left. Only one step used the numbers at all. Take the walls away and the same two numbers allow 34 different full lines (a computer count); the four walls cut that to one.
How Hard and Expert use walls
In Puzzle Picnic, Trail has walls on its two biggest levels: Hard is a 7x7 board with walls, and Expert is 8x8 with more walls; on both, the numbers are trimmed to the fewest that still give one solution. Easy (5x5) and Medium (6x6) have no walls, and rely on numbers alone. Each wall in the app is a short piece between two neighbouring squares, four of them on a Hard board and six on Expert, so long fences are rarer there than in some hand-made puzzles, and counting exits beside each piece is the tool you will use most. The trade is the one the worked puzzle shows. A number tells you one square's place in the order. A wall tells you that a link is missing, which can force the links of two squares and start a chain.
That changes how you read a hard board:
- Walls first, numbers second. Scan every wall and count exits on both sides of it. Mark any forced links before you look at the numbers.
- Corners and walls together. A corner next to a wall, or an edge square beside one, is where the first certain links usually are.
- Look for fences. If several walls line up, check whether they cut the board into parts with few gaps. Count the gaps and decide which side the line finishes on.
- Then the numbers. Use consecutive numbers to decide which way each forced piece runs, and refuse links between numbers that are not consecutive.
- Recount after every move. New line next to a wall turns more squares into two-exit squares.
Every Puzzle Picnic puzzle has exactly one solution, and a solver checks that before you see it, so on Hard and Expert there is always a certain next step. If you cannot find one, the place to look is almost always beside a wall.
Frequently asked questions
Can the line pass through a wall in Trail?
No. A wall sits between two squares, and the line can never step directly across it. Both squares still have to be on the line; it just has to reach them from another side.
Are walls in Trail squares the line has to avoid?
No. Trail's walls are thick lines along the sides of squares, not blocked squares. Every square of the board is still part of the line, which is why walls give information without taking squares away.
Which levels in Puzzle Picnic have walls?
Hard and Expert. Hard is a 7x7 board with walls, and Expert is 8x8 with more walls. Easy (5x5) and Medium (6x6) use numbers only, at least eight of them.
Why do puzzles with walls have fewer numbers?
A wall rules out routes the same way a number does. Each wall removes a possible link, and squares beside walls often have only two exits, which fixes their links. With enough walls, a few numbers are enough to leave exactly one solution.
Where to go next
Try a Hard board with the walls-first routine above, and recount exits beside each wall as you go. For the techniques that work on every board, read path puzzle strategies. For the maths of why removing links makes paths easier to find, see Hamiltonian paths explained, and for the sizes and levels, what changes at each level. Every Trail guide is on the Trail topic page, and a walled board to practise on is waiting on the Trail page.