Pipes

Start in the corners

Pipes hands you a scrambled plumbing job: every tile holds a straight, an elbow or a junction, and each click turns it 90 degrees. The quickest route to a clean solve is to ignore the messy middle and go straight for the corners. A corner tile can only face into the board, so an elbow there has exactly one legal rotation, and a straight pipe can't sit in a corner at all. Lock those down first. Every certain tile hands its neighbours a connector they must meet, and the solution spreads inward from the border like water finding its level.

The border does half the work

Edges are nearly as generous as corners, because no pipe may ever point off the board. Take a straight pipe on the top edge, away from a corner. Stand it upright and one end pokes off the board, which is illegal. So it must lie flat along the edge. One thought, tile solved. A three-way junction on that same edge is forced too: the only rotation that keeps all three arms in play is the one with its flat back against the border. Dead ends are the third gift, since a tile with a single connector wedged against the edge usually has only one direction that leads anywhere. Work the whole border like this before touching the middle and a third of the board often solves itself.

Then let the tiles talk to each other. Pipe ends must meet pipe ends: if your arm points at a neighbour, the neighbour must point back, or you've built a leak. The reverse matters just as much. When a neighbour shows you its blank side, your arm can't point there, and half the remaining rotations die on the spot.

No loops allowed

Here's the rule that trips people up: the finished network is one connected tree, not a web. Every endpoint links back to the source along exactly one path, which means a closed ring of pipe is always wrong. If you spot a loop feeding into itself, some tile in it is turned badly. There's a tidy bit of math behind this: a network that connects everything with no loops always has exactly one less link than it has pieces, so every loop you build means something else, somewhere, is cut off. That's why one wrong ring so often strands a far corner of the board.

The highlight is your honest friend here. Connected pipe lights up, so a dark tile in the middle of a solved-looking area is telling you something, and a glowing loop is over-connected by definition.

• Corners first, then edges, then dead ends, then the junctions in the middle.
• Each click is 90 degrees, so a tile is never more than three clicks from correct. If you've spun one five times, you're guessing, not solving.
• When two rotations both look legal, leave the tile and solve elsewhere. Its neighbours will usually make the choice for you.

When the board won't light

Late in a solve, the usual problem isn't a hard tile. It's one quiet mistake hiding in a sea of correct ones. Don't re-check everything. Walk the frontier instead: the border between lit pipe and dark pipe. The wrong tile is almost always sitting right on that line, because a correctly turned tile next to the lit network would already be glowing. Trace where the light stops, look at the two or three tiles at the boundary, and ask which of them is showing a blank side where a connector should be. Nine times out of ten, that's your culprit, and fixing it lights up a whole dark region at once.

An old desktop classic

Rotate-the-pipes puzzles have lived on computers for decades. The loud arcade cousin is Pipe Mania from 1989 (sold in America as Pipe Dream), where you lay pipe ahead of flowing goo with a clock screaming at you. The calm form you're playing is better known as Net, a quiet fixture of Linux desktops through games like KNetWalk and Simon Tatham's puzzle collection. No clock, no goo, just a spatial problem that clicks shut all at once when the last elbow turns. It scratches the same itch as untangling a pair of headphones, with the pleasant difference that this one always comes out clean.