Notes on this puzzle
11 clues around the edge, out of a possible 24, frame this 6×6 grid. 4 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 6. The bottom edge carries the most clues (4). 13 edge positions are blank, so parts of the grid are solved from the inside out.
Where to beginTry row 1, column 1 first: its row and column clues decide it without any other help. Check every pair of opposite clues; a pair adding up to N+1 is a gift.