They approach the Navel Gym gate, and Ash opens it. Inside, there is a cable car and a trail leading up the mountain. Pikachu points at a sign that explains challengers must climb up the mountain without using Pokémon, otherwise they risk disqualification, while spectators can use the cable car. Danny also climbs along, moving at a seemingly easy pace while Ash is struggling with both the exertion and a slight fear of heights. At one point, Misty and Tracey pass via the cable car, and Misty calls to Danny. This irritates and distracts Ash, which causes him to slip and fall down. He grabs onto a ledge and attempts to call out Bulbasaur, but Danny reminds him of the rule. Ash puts the Poké Ball back and manages to climb back up.
(Source: Bulbapedia)