Duncan spread his consciousness and enveloped the surrounding region as much as possible. He was currently seated in the middle of a cave that was hidden behind a hedge of overgrown wild plants.
Initially, he had tried sitting at the bottom of a hill or looking at it from a distance. But, soon Duncan found out that he wasn't able to elicit any feelings regarding the hills in front of him.
As a cultivator who was at the peak of the Spirit Sea realm, Duncan could extend his consciousness and perceive the surroundings easily. But, the range his consciousness could perceive was really limited.
The hills were big. They spanned miles in every direction from top to bottom. His meager consciousness couldn't envelop them and perceive them. This caused a huge issue in his effort to understand the qualities of the hill.