The Volcano
Lin Mu and Little Shrubby had a few battles during their travel to the volcano but were still unhurt. Though they were certainly tired. Normally such travel would not have exhausted them even if they traveled for over a month without stop.
But when one added battles against other Nascent soul realm beasts and core condensation realm beasts, it meant that their spirit Qi stores would be used up and slow them down.
They thus needed to take breaks from time to time to rest and recuperate before they could head on ahead. After all, if they tried to rush through without properly resting, they might be in greater danger than normal.
After all, the same attacks they faced could become deadly if they had no spirit Qi to defend with or deal with the situation appropriately. But on the plus side, this also gave them the opportunity to eat the beast corpses that they had obtained during this time.