tunnel, cave, catacomb, burrow, shaft, drift, adit, chunnel
A passage through a hill is typically called a tunnel. It is an underground passageway that cuts through the hill, allowing for easier transportation or access.
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.
An underground passage
Secret of the Underground Passage - 1911 was released on: USA: 14 October 1911
it means a secret passage
There is an underground passage in Washington DC. This is in place in case of an emergency so that the President and important staff can go there if the need arises.
It's a small passage
It's a cave.
it was a passage way for slaves to get to the north.
The under ground passage in a ringfort is called a souterain. These may have been used to store food or to hide during raids. There is one nearby which links up two areas.
A horizontal mine shaft is called an adit. It is a passage or tunnel that connects the surface with underground mine workings for access, ventilation, and transportation of materials.
A river that flows into an underground passage or sinkhole.