The growth of the Kodokan tracks the growth of judo itself. From the original twelve mats at the Eishoji temple, the school expanded to 40 mats by 1887, then 107 by 1894, 314 by 1898, and 986 when it moved to its current Bunkyo location in 1958. Each move reflected a martial art outgrowing its walls. The current building houses five main dojo: the Main, School, International, Women's, and Boys' training halls, plus a special dojo reserved for retired judoka and advanced technique study. The Main Dojo occupies the entire seventh floor, its 420 mats precisely calibrated for the right amount of floor spring, the kind of engineering detail that matters when bodies are being thrown repeatedly. Four official contests can run simultaneously on that floor, watched by up to 900 spectators seated on the eighth floor above.

Women have trained at the Kodokan since 1926, but always in a separate group and with a glass ceiling fixed at the 5th dan rank. That began to change in 1962 when Rena Kanokogi, an American judoka, so thoroughly dominated the other students in the women's training sessions that she became the first woman permitted to train in the men's group. A decade later, Keiko Fukuda and her senior Masako Noritomi launched a letter-writing campaign against the rule capping women's advancement. In November 1972, both were promoted to 6th dan, shattering a barrier that had stood for nearly half a century. Fukuda kept climbing. In 1994, at the age of 81, she became the first woman in history to receive a red belt from the Kodokan, marking the rarified 8th dan rank. Her persistence helped reshape the institution from within, proving that the gentle way had room for everyone.

The Kodokan is not merely a gym. Its second floor houses the Kano Memorial Hall, with photographs, documents, and artifacts tracing both the life of the founder and the global spread of his art. The research wing contains four laboratories dedicated to distinct aspects of judo study: theoretical and historical research, psychological analysis, technical and physical-strength assessment, and physiological investigation. The library holds over 7,000 books. The building's third floor includes residential quarters for judoka living and training at the institute, maintaining Kano's original vision of judo as a complete educational system rather than just a sport. The research staff collaborates with international scholars and opens its findings to the public once a year, free of charge.

Visitors to Tokyo can walk into the Kodokan and watch practice from the spectator level on the eighth floor. Those who want to step onto the mats need permission, though one-time visitors are often welcomed into randori, or free practice sessions, with international students. There is one absolute rule: only white judogi are permitted. No blue uniforms, no colored belts on the jackets, no undershirts for men. The white judogi is not a preference but a principle, rooted in Kano's belief that judo training should strip away external distinctions. At the Kodokan, the mat is a leveler. The building that began as twelve borrowed mats in a temple still operates on its founder's conviction that the way is best studied in simplicity, and that the path from student to master runs through discipline, not decoration.