See more discussion of the puzzles from the United States’ 2021 Puzzle Grand Prix on this post. Note there are some construction details and potential spoilers on that post so view it after you solve.

PDF

or solve online (using our beta test of Penpa-Edit tools in linex mode where left click+drag draws lines and right click marks X’s)

Author/Opus: This is the 398th puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Standard Castle Wall rules.

Difficulty: 2 stars (estimate based off competition points; timing standards not available from our usual testers)

Solution: PDF

Note: Follow this link for more Castle Wall puzzles. If you are new to this puzzle type, here are our easiest Castle Wall puzzles to get started on. More Castle Wall puzzles can be found in our beginner-friendly collection Intro to GMPuzzles as well as the larger collection Castle Wall, both by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools in linex mode where left click+drag draws lines and right click marks X’s)

Theme: Twos

Author/Opus: This is the 28th puzzle from guest contributor Joseph Howard.

Rules: Standard Castle Wall rules.

Difficulty: 4 stars

Time Standards (highlight to view): Grandmaster = 5:15, Master = 10:15, Expert = 20:30

Solution: PDF; a solution video is also available here.

Note: Follow this link for more Castle Wall puzzles. If you are new to this puzzle type, here are our easiest Castle Wall puzzles to get started on. More Castle Wall puzzles can be found in our beginner-friendly collection Intro to GMPuzzles as well as the larger collection Castle Wall, both by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools in linex mode where left click+drag draws lines and right click marks X’s)

Theme: Slanted Squares

Author/Opus: This is the 2nd puzzle from guest contributor Mark Sweep.

Rules: Standard Castle Wall rules, but none of the clue colors are given. The solver should determine whether each gray clue is white or black. Also, the loop must go straight through the cells with white circles, with a turn in at least one of the cells immediately before/after each white circle. The loop must make a turn in all the black circles, but must go straight in both cells immediately before/after each black circle.

Difficulty: 3.5 stars

Time Standards (highlight to view): Grandmaster = 5:15, Master = 8:00, Expert = 16:00

Solution: PDF; a solution video is also available here.

Note: Follow this link for more Castle Wall puzzles. If you are new to this puzzle type, here are our easiest Castle Wall puzzles to get started on. More Castle Wall puzzles can be found in our beginner-friendly collection Intro to GMPuzzles as well as the larger collection Castle Wall, both by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools in linex mode where left click+drag draws lines and right click marks X’s)

Theme: Black Mirror

Author/Opus: This is the 337th puzzle from our managing editor Serkan Yürekli.

Rules: Standard Castle Wall rules.

Difficulty: 3 stars

Time Standards (highlight to view): Grandmaster = 3:30, Master = 4:30, Expert = 9:00

Solution: PDF; a solution video is also available here.

Note: Follow this link for more Castle Wall puzzles. If you are new to this puzzle type, here are our easiest Castle Wall puzzles to get started on. More Castle Wall puzzles can be found in our beginner-friendly collection Intro to GMPuzzles as well as the larger collection Castle Wall, both by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools in linex mode where left click+drag draws lines and right click marks X’s)

Theme: Slanted Squares

Author/Opus: This is the 29th puzzle from our contributing puzzlemaster JinHoo Ahn.

Rules: Standard Castle Wall rules.

Difficulty: 2.5 stars

Time Standards (highlight to view): Grandmaster = 2:00, Master = 3:00, Expert = 6:00

Solution: PDF; a solution video is also available here.

Note: Follow this link for more Castle Wall puzzles. If you are new to this puzzle type, here are our easiest Castle Wall puzzles to get started on. More Castle Wall puzzles can be found in our beginner-friendly collection Intro to GMPuzzles as well as the larger collection Castle Wall, both by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools in linex mode where left click+drag draws lines and right click marks X’s)

Theme: One True King

Author/Opus: This is the 213th puzzle from our contributing puzzlemaster Prasanna Seshadri.

Rules: Standard Castle Wall rules.

Difficulty: 2 stars

Time Standards (highlight to view): Grandmaster = 1:15, Master = 2:00, Expert = 4:00

Solution: PDF; a solution video is also available here.

Note: Follow this link for more Castle Wall puzzles. If you are new to this puzzle type, here are our easiest Castle Wall puzzles to get started on. More Castle Wall puzzles can be found in our beginner-friendly collection Intro to GMPuzzles as well as the larger collection Castle Wall, both by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools in linex mode where left click+drag draws lines and right click marks X’s)

Theme: One Gear

Author/Opus: This is the 204th puzzle from our contributing puzzlemaster Murat Can Tonta.

Rules: Standard Castle Wall rules.

Difficulty: 1 star

Time Standards (highlight to view): Grandmaster = 0:40, Master = 1:00, Expert = 2:00

Solution: PDF; a solution video is also available here.

Note: Follow this link for more Castle Wall puzzles. If you are new to this puzzle type, here are our easiest Castle Wall puzzles to get started on. More Castle Wall puzzles can be found in our beginner-friendly collection Intro to GMPuzzles as well as the larger collection Castle Wall, both by Serkan Yürekli.

From Prasanna: “This puzzle is meant to be a culmination of 10 years of authoring puzzles. I want to especially thank GMPuzzles for accommodating these special puzzles every year even if it may not have fit the regular schedules. I also see this puzzle as a “reset” of sorts, and I’ll get back to simple ideas to celebrate my next few birthdays, and then see where that takes me. These last 10 years have been a fantastic experience and I’d like to take this moment to thank the puzzle community as a whole for being a huge part of my journey.”

(view directly for a larger image)

PDF

or solve online (using our beta test of Penpa-Edit tools; note that the default puzzle info is too long — even for an url shortener — so copy and paste all the text in this file into the “Load” option in the upper-right of the penpa-edit interface to access.)

Theme: The Journey

Author/Opus: This is the 201st puzzle from our contributing puzzlemaster Prasanna Seshadri.

Rules: Please see first two pages of the PDF for a detailed description of the rules and more background on the theme of the puzzle.

Difficulty: 5 stars?

Solution: PDF

PDF

or solve online (using our beta test of Penpa-Edit tools in linex mode where left click+drag draws lines and right click marks X’s)

Theme: Clue Symmetry and Logic

Author/Opus: This is the 146th puzzle from our contributing puzzlemaster Murat Can Tonta.

Rules: Standard Castle Wall rules.

Answer String: Enter the length in cells of the horizontal loop segments from left to right in the marked rows, starting at the top. If the loop only has vertical segments in the marked row, enter 0. Separate each row’s entry with a comma.

Time Standards (highlight to view): Grandmaster = 5:00, Master = 7:30, Expert = 15:00

Solution: PDF

Note: Follow this link for more Castle Wall puzzles. If you are new to this puzzle type, here are our easiest Castle Wall puzzles to get started on. More Castle Wall puzzles can be found in our beginner-friendly collection Intro to GMPuzzles as well as the larger collection Castle Wall, both by Serkan Yürekli.

PDF

or solve online (using our beta test of Penpa-Edit tools in linex mode where left click+drag draws lines and right click marks X’s)

Theme: Windmill

Author/Opus: This is the 19th puzzle from guest contributor Ashish Kumar.

Rules: Standard Castle Wall rules, but none of the clue colors are given. For each symmetric pair of clue cells (reflecting through the center of the grid), one cell is white and the other cell is black.

Answer String: Enter the length in cells of the horizontal loop segments from left to right in the marked rows, starting at the top. If the loop only has vertical segments in the marked row, enter 0. Separate each row’s entry with a comma.

Time Standards (highlight to view): Grandmaster = 4:45, Master = 6:30, Expert = 13:00

Solution: PDF

Note: Follow this link for more Castle Wall puzzles. If you are new to this puzzle type, here are our easiest Castle Wall puzzles to get started on. More Castle Wall puzzles can be found in our beginner-friendly collection Intro to GMPuzzles as well as the larger collection Castle Wall, both by Serkan Yürekli.