Normal sudoku rules apply. Shade some cells (walls) such that they form orthogonally connected regions that must touch an edge of the grid. Similarly, leave some cells unshaded (tunnel) to form a single orthogonally connected path, which may not touch itself diagonally and does not branch. No 2x2 area of the grid may be completely shaded or unshaded. Cells marked with a square indicate how many cells (including themselves) they see orthogonally (walls block their view, but they may themselves be walls). White dots indicate consecutive digits along the path (all white dots are shown). Black dots indicate that cells are in a 1:2 ratio within the wall (all black dots are shown). Note that dots do not disclose relationships between shaded and unshaded cells.