Cave
A cave, cavern or grotto, was a hollow passage , usually with an opening to the surface. They are found on planets throughout the Milky Way Galaxy. 

Troglodyte was a term meaning cave-dweller. ()

Caves could be natural or artificial. Natural caves could be formed by water or lava flows. Ice caves also existed. (; ; )

Caves could make excellent hiding locations, as the rocks and ores in the walls could stop sensors from penetrating them. They also made excellent shelters from the outside environments. For example, Data, Riker, and Doctor Crusher led the colonists on Melona IV to shelter in caves to escape the destruction of the Crystalline Entity. (; ; ; )

They were also useful hiding places. After the Vaadwaur homeworld was bombarded from orbit in the 15th century, one battalion managed to survive in an underground cavern. () The unification movement on Romulus made use of a cave as a base of operation. () In 2371, a cave system on Avery III hid a Vidiian base. ()

Native Americans often used caves as shelters during their vision quests. ()

On Sigma Draconis VI, caves lead into an underground complex established before the decline of its civilization. ()

The Shore Leave Planet, while artificial, featured caves. ()

Mintaka III exhibited karst topography, which included sinkholes, underground rivers and caverns. ()

While Spock and Leonard McCoy were trapped in a Sarpeidon ice age, they took shelter in a cave. ()

After an asteroid hit Terra Nova in 2083, survivors fled to the planet's caves and tunnel systems and eventually adapted to underground existence. Some caves were used as gutting rooms and wells. ()

While exploring Archer IV in 2151, a cavern was found. This turned out to be fortunate, as a storm stranded several the  crew members who then sought shelter there. ()

 featured a cave system stretching over at least fifty kilometers. At the time of the 2153 regime change, a Denobulan Science Academy team was studying the caves. ()

While on Capella IV in 2267, Enterprise crewmembers took shelter in a cave. ()

After being attacked by a mugato on Neural in 2268, James T. Kirk was treated in a cave. ()

There was a cave near the Starnes Exploration Party on Triacus, which gave off strange tricorder readings implied to be associated with Gorgan. ()

In 2285, it was revealed that the Starfleet Corps of Engineers had spent ten months excavating a massive cave system on Regula, while a matrix to terraform the caves needed only a day. ()

In 2351, a ten-year-old Julian Bashir and his father Richard were trapped in a cave on Invernia II by a storm. ()

In 2366, after being stranded on Galorndon Core, Geordi La Forge and Bochra were forced to find shelter in a cave. ()

In 2367, Jean-Luc Picard, Wesley Crusher, and Dirgo crash landed on Lambda Paz and ultimately sought shelter in a cave. ()

In 2373, a group of Maquis refugees had moved to Marva IV, where they lived in caves. ()

In 2373, the crew of the  encountered a large cave-dwelling creature that ate humanoids, the Hanonian land eel. ()

B'Elanna Torres' holographic program Torres 216 was set in a cave. ()

Caves of note
Carlsbad Caverns
Cavern of Despair (mythological)
Caves of Kahless
Caves of Mak'ala
Caves of No'Mat
Caves of Touth
Ceremonial chamber
Fire Caves
Genesis cave
Ice Caves of Etheenia
No'Mat lava caves
Osana caverns

Cave-dwelling lifeforms 
Alvanian cave sloth
Cave dweller
Cave-rat
Cave-wasp
Hanonian land eel
Ice-bore
Lynar

Sentient
Horta
Loque'eque
Novan
Ocampan

See also
Sentient cave
Speleothem
Lava tube
A Cave Beyond Logic: Vulcan Perspectives on Platonic Thought

External link
 

de:Höhle
Landforms