reaches
n. C / Un. the most distant or hidden parts of a place, like a river or a large organization. You use this to talk about areas that are far away or hard to get to.
n. the remote or distant parts of an area, river, or abstract system. Plural in form and typically used to describe the furthest extent of a territory or the deep levels of a hierarchy.
The explorers traveled to the upper reaches of the river.
Scientists are still discovering new species in the deepest reaches of the ocean where sunlight never penetrates.
The investigation eventually extended into the highest reaches of the government, uncovering a network of influence that had remained hidden for decades.
Almost always used in the plural form ('reaches') when referring to geographic or metaphorical distances.