The origin of this puzzle is not known, but it appears to have first been published by Nikoli.
Puzzle and Goal
An unsolved puzzle consists of a rectangular grid divided into regions.
The goal is to create a single closed loop according to the rules.
The solved grid must satisfy the following conditions:
The loop must enter and exit each region exactly once.
Not all cells need to be visited; however, unvisited cells in different regions cannot be orthogonal neighbors.