Normal sudoku rules apply. Shade some cells such that all shaded cells are orthogonally connected and all unshaded cells are orthogonally connected. No 2x2 area may be fully shaded or fully unshaded. If two digits are separated by a black dot one digit is double the other. Additionally, a black dot always separates a shaded and an unshaded cell. Not all dots are necessarily given. Shaded digits in the grid represent skyscrapers of that height, with taller skyscrapers obscuring smaller ones. A clue outside the grid shows the number of all visible skyscrapers from the clue's direction. Unshaded digits do not affect the outside clues.