A "narrow gorge" refers to a small, tight passage or valley usually between mountains or cliffs. It is a long, deep space that is slender or restricted in width, making it difficult for people or objects to pass through easily. Full definition
Crawford Notch is the steep and narrow gorge of the Saco River in the White Mountains of New Hampshire and it was discovered in 1771 as being a route through the mountains, which until then had been thought to be impenetrable; the idea of putting a railway through the area was considered a difficult engineering feat that many thought to be impossible. (raildiscoveries.com)
The route leads through narrow gorges and passes by quaint Andean towns. (anywhere.com)
Today these rivers lie in narrow gorges cut across these growing folds. (sciencedaily.com)