The rules
- Draw one closed loop along the grid lines, from dot to dot.
- A number says how many of its cell's four sides the loop runs along.
- The loop never branches and never crosses itself: every dot has two lines or none.
How to play here
Tap an edge to draw a line, again to cross it out, again to clear it. Drag along the edges to draw in one stroke.
Three ways to play
Campaign
Chapters that start gently and bring in one new idea at a time.
Daily puzzle
A new board every day, the same for everyone. Solve every one in a month and that month's trophy is yours.
Endless
Keep going as long as you like, in Easy, Medium, Hard and Expert.
Common questions
Is Sulcus free?
Yes. You can play here without paying and without an account. Ads keep the lights on.
Where is my progress saved?
In this browser, on this device. If you clear the site data, your progress goes with it. A free Solvarium account keeps it safe.
Does it work on a phone or tablet?
Yes. It runs in any current browser on phones, tablets and computers, and the board resizes to fit the screen.
Does every puzzle really have one solution?
Yes. Every board goes through a solver before it ships, and anything with more than one solution is thrown out.