Peak Sudoku
Fish, wings, chains & uniquenessPeak Score 60–75

Skyscraper

Two rows (or columns) where a digit has exactly two positions, sharing one column (or row).

Also known as: Turbot Fish Type 1, Single-Digit Chain

Quick Summary

A Skyscraper occurs when two rows have a target candidate in exactly two cells each, and two of those cells share a column (the base). At least one of the other two cells (the roofs) must hold that digit.

Understanding the Skyscraper Technique

The Skyscraper is a single-digit pattern from the Turbot Fish family. Think of it as an X-Wing that got knocked askew: in two rows, a target digit appears exactly twice. One end of each row lines up in the same column (forming the shared 'base'), while the other two ends ('roofs') do not line up. Because the base column can only contain one instance of the digit, at least one of the two roof cells must contain it. Any cell that sees both roof cells cannot contain that candidate.

Visual Examples

Green cells highlight the Skyscraper pattern, amber cells denote where candidates are affected, and struck-through pencil marks show the eliminations. Use the buttons or arrow keys to browse examples.

Example 1 of 5
In columns 6 and 9, the digit 3 fits in only two cells each, and they share row 4. Only one of the two row 4 cells can be 3, so one of the far ends (R7C6 or R9C9) must be 3. Any cell that sees both ends can drop 3.
Removes: 3 from R9C5, R7C8

How to Spot & Solve a Skyscraper (Step-by-Step Guide)

The complete visual scanning and logical deduction process to execute this technique:

  • 1Pick a digit and find two parallel rows where that digit appears in exactly two cells each.
  • 2Notice that one end of each row shares the same column (the base), while the opposite ends sit in different columns (the roofs).
  • 3Because the base column can only hold the digit once, at least one of the base cells must be false.
  • 4If a base cell is false, the opposite roof cell in that row is forced to be true.
  • 5Therefore, at least one of the two roof cells is guaranteed to hold the digit.
  • 6Eliminate that candidate from any cell that has a direct line of sight to both roof cells.

Common Traps & Mistakes to Avoid

  • Allowing extra candidates in the base rows.
  • Eliminating candidates that only see one of the roof cells.
  • Forgetting that Skyscraper can also operate vertically (two columns with a shared row base).

Frequently Asked Questions

How is a Skyscraper different from an X-Wing?

In an X-Wing, both ends line up in the same two columns. In a Skyscraper, only one end lines up; the other two ends are offset in different columns.

Expand your repertoire by learning prerequisites and advanced counterparts:

2-String KitePeak Score 60–75

One strong link on a row and one on a column, sharing a cell in the same box.

Read guide →
X-WingPeak Score 55–70

A digit restricted to exactly two cells in two different rows, forming a rectangle.

Read guide →
W-WingPeak Score 65–80

Two bivalue cells with identical candidates, bridged by a strong link on one digit.

Read guide →

Ready to Practice Skyscraper?

Try a puzzle in the Tough tier (Peak Score 61–70), or browse all 25 techniques.

Play Tough puzzleAll 25 techniques