Dead Ends
a dead end is ok. back up and keep trying.
a hand-drawn maze with counted dead ends: draw from start to end without crossing a line, backing out of each dead end you meet
From Daniel Fabe Schmidt's book Maze Structure: a dead end is not a mistake, it is one wrong way you no longer have to try. Each level says how many it has; back out of each one you meet and the maze gets smaller.
Concepts: mazes, graphs, puzzles.
An interactive you play with one thumb, on Wundr.