  We overview experimental laboratory prototypes of maze solvers. We speculate
that all maze solvers implement Lee algorithm by first developing a gradient of
values showing a distance from any site of the maze to the destination site and
then tracing a path from a given source site to the destination site. All
prototypes approximate a set of many-source-one-destination paths using
resistance, chemical and temporal gradients. They trace a path from a given
source site to the destination site using electrical current, fluidic, growth
of slime mould, Marangoni flow, crawling of epithelial cells, excitation waves
in chemical medium, propagating crystallisation patterns. Some of the
prototypes visualise the path using a stream of dye, thermal camera or glow
discharge; others require a computer to extract the path from time lapse images
of the tracing. We discuss the prototypes in terms of speed, costs and
durability of the path visualisation.
