Castle Wall

Rules

Draw a single closed loop passing through some empty cells in the grid. The loop connects centers of adjacent cells, makes only right-angle turns or goes straight, and does not intersect or cross itself. The grid contains some bordered or black cells that cannot be part of the loop. Bordered cells must be inside the loop; black cells must be outside the loop. Numbers and arrows refer to the total sum of the lengths of straight loop segments along the given direction. (An equivalent way to understand these values is by putting a dot each place the loop crosses a cell border. Each numbered arrow then points to that number of dots.)

(Rules from PGP IB)

Rule Variations

• Some puzzles include grey cells. They can be on either side of the loop.

History of the puzzle

Invented by Palmer Mebane (USA) in 2009. His first puzzle can be seen in his old blog.

Variants

Total Castle Wall

First appeared on WPC 2019. The author was Jürgen Blume-Nienhaus (Germany).

Draw a closed loop into the grid that runs horizontally and vertically and passes through each cell at most once. Black cells must be outside the loop, white cells with heavy borders must be inside the loop; this includes marked cells with and without numbers. The numbers indicate the total length of all horizontal loop segments in the respective row plus the total length of all vertical loop segments in the respective column.

Appearances in the past WPCs

• WPC 2019/World Cup Round 2 by Jürgen Blume-Nienhaus
• WPC 2019/Team Playoffs by Jürgen Blume-Nienhaus
• WPC 2018/Round 7 by Jan Zvěřina
• WPC 2017/Round 8 by Prasanna Seshadri