There where 53 Post Towns (rest stops) on the Old Tokaido route between Edo (modern Tokyo) and Kyoto. Adding the starting point of Nihonbashi (in Edo) and the end point of Kyoto makes 55. Edo Period’s second Shogun (Tokugawa Hidetada) extended Tokaido from Kyoto to Osaka, increasing the total number of Post Towns to 57. The modern Tokaido train line follows the Old Tokaido closely, although there are some helpful additions including Atami, a possible starting point for Hakone Hachiri Tour , and Shin-Osaka.
Check below blog posts for more information on specific Post Towns (numbering uses standard convention of placing Tokaido departure point, Nihonbashi in Tokyo, at #0):
Blog posts eventually to come on other post towns of Nihonbashi, Shinagawa, Kawasaki, Kanagawa, Totsuka, Fujisawa, Hiratsuka, Oiso, Numazu, Hara, Yoshiwara, Okitsu, Eijiro, Okabe, Fujieda, Shimada, Mitsuke, Maisaka, Shirasuka, Futagawa, Okazaki, Chiryu, Narumi, Miya, Kuwana, Yokaichi, Ishiyakushi, Shouno, Kameyama, Seki, Sakanoshita, Tsuchiyama, Minakuchi, Ishibe, Kusatsu, Ootsu, Fushimi, Yodo, Maigata, Muroguchi