Place numbers from 1-N in all the empty cells in the grid so that the numbers do not repeat in any outlined region and along the four grey lines. Each region has a unique path going through all cells in the region. Among such path, the relation between neighbouring numbers alternates between higher and lower. The same numbers may not touch each other not even diagonally.
(Example from WPC 2018 IB)
History of the puzzle
The idea was invented by František Luskač (Czech Rep.). Although it appeared in WPC 2018/Round 12, an "innovative" round, a hexagonal version of this puzzle was present in 2017 Czech Nationals under the name "Žížaly v Šestiúhelníku" ("Worms in a Hexagon").  Its exact first appearance is currently unknown.