Normal sudoku rules apply. Each letter from ABCDEFGHZ stands for a different digit from 1-9. Each labeled gray letter cell in the grid contains that digit. Where a ? is used, it always represents a two digit total. Ie the leading question mark is never 0. Digits in cages sum to the total given. Digits cannot repeat within cages. Digits along indicated diagonals have the indicated sum. Digits may repeat along such diagonals. Circles within the grid are quadruples. The indicated digit appears in at least one of the four surrounding cells. Digits with a door are numbered rooms. The indicated digit appears a number of cells into that row or column given by the first number in that row/column. Digits with a building are skyscrapers. They indicate how many digits are seen from the perspective of the clue if digits are only seen if they are the highest digit encountered so far.