This is so cool: graphical [Wayback/Archive] Introduction to the A* Algorithm
It is still being updated, which is even cooler:
Created 26 May 2014, updated Aug 2014, Feb 2016, Jun 2016, Jun 2020, Jul 2023
These are for general graph traversal. That Wikipedia article only mentions depth-first search and breadth-first search, but forgets the A* search algorithm which is an extension of the also not mentioned Dijkstra’s algorithm which in turn is based on breadth-first search.
The visualisations cover the breadth-first algorithms.
The example code is Python based, but easy to translate into other languages.
The visualisation code is in JavaScript, using these files (they Archive.is versions are more accurate than the Wayback Machine ones):
The Wiert Corner - irregular stream of stuff 