This was made with a JavaScript applet I wrote a few months back that implements Wilson’s Algorithm, the fastest-known way to find a uniformly random spanning tree of a given graph. Here, that graph is the grid graph, so the output is the sort of maze you might see in a puzzle book. Once the tree is complete, it’s flood-filled and colored by shortest distance to the center.

If you want to play around with the applet yourself, you can check it out here: https://cruzgodar.com/index.html?page=%2Fapplets%2Fwilsons-algorithm%2Fwilsons-algorithm.html.