One Stroke

Draw the whole figure in one continuous stroke — every line exactly once, never lifting your finger, never crossing a line. Solve a level to unlock the next.

There is a rule behind which figures can be drawn at all, and it is worth knowing: count the points where an odd number of lines meet. If there are none, start anywhere. If there are exactly two, you must start at one of them and you will finish at the other. Any more than two and the figure cannot be done in one stroke — so every level here has none or two.