Arto Inkala’s “Everest” Sudoku — Play It Online, With the Full Solution

Updated 15 October 2026

“Everest” is the 21-clue sudoku Arto Inkala published in 2012 as the world’s hardest, the follow-up to his 2006 AI Escargot. The nickname comes from the solving community, and it stuck because the puzzle sits at the very top of the difficulty scale. Play the original grid below, print it, or read the engine’s step-by-step solution further down.

Clues

21

Published SE rating

SE 11.9

Suuudokuuu rater

8.5+, past every implemented technique

Play Everest in the appPrint Everest — PDF with the solution

Where Everest comes from

Inkala presented the puzzle as harder than AI Escargot, and it was widely reprinted as the hardest sudoku ever made. Independent raters agree it is a big step up: Sudoku Explainer style tools place it around SE 11.9, against roughly 10.6 for AI Escargot, which puts it level with Golden Nugget at the top of the scale the difficulty rating guide explains. At this height different rating programs disagree by several tenths, depending on which chain types they model.

Source: SudokuWiki, “Arto Inkala Sudoku”. The rating is the published figure the Infinity corpus carries, not a Suuudokuuu measurement; see the hardest sudoku puzzles page for the other record grids.

The Everest solution, step by step

Suuudokuuu’s source-available engine solves Everest in 114 steps, reaching for the cheapest technique that still makes progress, exactly as it does when it rates a puzzle. 24 of those steps are forcing chains: the engine assumes a candidate, follows its consequences until something breaks, and removes the assumption. At 2 points even that runs dry — no technique the engine implements moves the grid — and the walkthrough says so, fills the cell with the fewest candidates from the verified solution, and carries on with logic from there. Every other step is a named deduction you can check by hand.

Along the way the walkthrough uses Full House, Naked Single, Hidden Single, Pointing Pair, Box Line Reduction, Naked Pair, Naked Triple, Hidden Pair, Hidden Triple, X-Wing, Swordfish, Finned Swordfish, Sashimi X-Wing, XY-Chain, Unique Rectangle and Nishio Forcing Chain.