Skyscraper
Advanced Logic22 / 32Two towers on one base — at least one roof is true.
Take a digit with exactly two candidates in each of two columns. If one end of each column lines up in the same row — the shared base — the two remaining ends form the roofs of two towers of different heights.
The base cells can't both hold the digit, so at least one tower is 'capped': one of the two roofs is true. Any cell that sees both roofs loses the digit.
See it in action
Step 1 of 4
The setup
For one digit, find columns (or rows) with exactly two candidates. Two such lines whose lower ends share a row are your towers — check what sees both upper ends. Step through this real position to see it happen.
Practice
Find the Skyscraper and remove its digit from the cells that see both roof ends.
Drill 1 of 29Tap a cell, then the candidate digit you want to remove.