What is a deep, narrow passage with steep rocky sides called?

A deep, narrow passage with steep rocky sides is referred to as a gorge. This term specifically describes a landform that is typically formed by the erosion of river waters over time, leading to the creation of steep cliffs on either side of a narrow valley. Gorges often provide dramatic landscapes and are characterized by their steep walls and significant depth.

In contrast, a gully is generally a smaller, shallower channel that can be formed by water runoff and often does not have the same level of steepness or depth as a gorge. A glade is an open space in a forest, often characterized by a lack of trees, and does not refer to a narrow passage. A gliff is not a standard term in geography, possibly a misspelling of 'cliff', which refers to vertical rock faces, but does not specifically describe a passage. Therefore, the most accurate term for a deep, narrow passage with steep rocky sides is indeed a gorge.