A passage through a hill ; underground, is called a TUNNEL.
However, a passage between two hills (surface) is a VALLEY.
A passage between two hills is dependent on its width. If the hills are low and far apart, then it is a VALE. However, if the hills are high and close together then it is a GLEN or RAVINE, or GORGE.
England, France, and The Netherlands competed to discover it. The route was called the North-West Passage
The word to describe a material that does not does not allow the passage of water through it is impermeable. In hydro-geological terms it may also be described as an aquiclude.
transport
conduit
butte
A tunnel
It is a tunnel.
A trail
To enter through the back secret passage of the hill.
A valley.
bone marrow.
Plasmodesmata.
osmosis
it could be a valley or a gorge
The Northwest Passage Apex;;;
Smoothing an object's shape is called streamlining. It is used for improving passage through air as well as water.
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