Snake Way

Snake Way, or Serpent Road, is legended to be one million kilometer long (621,371.192 miles). It is a narrow, winding path located in Other World above Hell, which leads from Lord Emna's check-in station to Kaio-Sama's planet and is the only method of getting to the latter (other than teleporting).

Only six people have known to cross the road in the manga: Lord Enma, Son Goku, Yamcha, Tenshinhan, Chaozu and Piccolo. Kaio-sama himself had to travel backwards on the road after Cell blew up his planet.

Overview
Snake Way begins at Lord Enma's castle and ends at Kaio-Sama's Planet. The path is surrounded by a thin layer of yellow clouds, under them is Hell. If someone falls through the clouds they cannot go back through them. Goku falls off Snake Way when trying to get to Kaio-Sama's Planet. Goku is only able to get out when he competes with two ogres, but is forced to start back at the beginning of Snake Way. After reaching the end of Snake Way and completing his training with Kaio-Sama, he travels back on Snake Way; making the entire journey in only one day, compared to the 177 days it took the first time.

While fighting with the Saiyans, Piccolo, Tenshinhan, Yamcha, and Chaozu are killed. They, too, travel down Snake Way to train with Kaio-Sama. Kaio-Sama proclaims that they all reached his planet faster than Goku did, since they have become stronger since the fight with Raditz.

After Cell blows up King Kai's Planet, Bubbles, Goku, and Kaio-Sama himself all travel down Snake Way towards Lord Enma's castle.

Anime Filler
A lot of filler was added to Goku running along Snake Way during his first trip to Kaio-Sama's planet. Much of this filler was just extra clips of Goku running down Snake Way to pad out an episode, however other episodes contained entire plots from filler created during Goku's journey.

Also since Gregory is an anime only character the simple fact that he is present on the road after Cell blows up is only in the anime.