Fortunately for us there is historical film footage of both Jigoro Kano and Kyozu Mifune that are a joy to watch and learn from. These visual references offer the serious student a wealth of quality information if they are diligent, particularily if they explore Variation (Henka) related to their martial art. Look them up on Youtube
While following the footage there are many avenues of exploration in techniques that can be used in your own study. They have definitely expanded my understanding of Technique (Waza), Collapsing Structure (Kuzushi), Timing (Hyoshi), and helped me understand my own Kata.