Gradient Golf is a free interactive game that teaches gradient descent - the most important optimization algorithm in machine learning. You see a colorful loss landscape (dark blue = low, red = high) and your goal is to guide a ball to the deepest valley.
Each level introduces a new optimization challenge: ill-conditioned valleys, saddle points, local minima, noisy surfaces, and more. Choose your starting position and learning rate carefully - a rate too high will overshoot, too low will stall. Later levels unlock momentum, showing how it helps escape flat regions and narrow ravines.
Want the full theory? Read the Complete Guide to Gradient Descent.