Normal sudoku rules apply. In addition, some cells must be colored grey so that all grey cells (the "walls") are orthogonally connected to the edge and all other cells form an orthogonally connected area (the "cave"). Each yellow marked cell is inside the cave and its digit indicates how many cave cells can be seen horizontally and vertically before hitting a wall or the edge of the grid. The clue cell itself is counted for this purpose. The digit in some yellow cells has yet to be determined and not every possible clue cell is given. In an orthogonally connected area of grey cells no digits may repeat. 2x2 blocks of either cave or wall are possible.