This blog post has a nice visualization of sudoku solving using backtracking. https://medium.com/analytics-vidhya/sudoku-backtracking-algo...

Although the case they use is almost perversely simple. Imagine in a 'real' sudoku that each number might need to be backtracked multiple times, such that the algorithm is regularly going almost back to the start.

Edit: here's a classic one trying to solve the 8 queens problem: https://commons.wikimedia.org/wiki/File:Eight-queens-animati...