Notes on this puzzle
Skyscrapers #5406 is a 7×7 city: every row and column holds the heights 1 to 7 once, and 14 of the 28 edge positions carry a clue. 2 heights are already standing inside the grid.
There is 1 clue of 1 around the frame; the first cell beside each of them must hold a 7. The bottom edge carries the most clues (4). 14 edge positions are blank, so parts of the grid are solved from the inside out.
Where to beginTry row 5, column 1 first: its row and column clues decide it without any other help. Use notes for the heights 6 and 7 first; once they are placed, the lower heights follow.