洞穴

，世界最大的地下自然洞穴]]

洞穴（洞、洞窟）是指地底的通道或空間，可進入其中，形成方式可能是水的侵蝕作用，或是風與微生物等其他外力的風化作用。許多自然界的洞穴是形成於石灰岩地帶，為溶洞（鐘乳洞）。全球约有180万个洞穴。

根据光照强度，洞穴可大致分为三个区域：洞口带、弱光带和黑暗带。

人工洞穴
人类为商业、交通而开挖的洞穴，包含了隧道，人行地下道、下水道、防空洞等。

參見
*坑洞
*洞穴學
*洞穴探險
*地下瀑布
*地穴寓言

参考文献
外部連結

• [https://www.caves.org.au Australian Speleological Federation (ASF)] , AU
• [https://www.british-caving.org.uk/ British Caving Association (BCA)] , UK
• [https://www.showcaves.com/english/explain/Speleology/Classification.html Classification of Caves] A list of cave types with links to further information
• [http://www.caves.org/pub/journal/ Journal of Cave and Karst Studies]
• [http://www.caves.org/ National Speleological Society (NSS)] , US
• [https://www.uis-speleo.org/ International Union of Speleology (UIS)] .
• [http://www.ssslib.ch/bbs/ Speleological Abstract (SA/BBS)] An annual review of the world's speleological literature.
• [http://www.goodearthgraphics.com/virtcave The Virtual Cave] Photographs of many types of caves.
• [http://www.cave-biology.org/ Welcome to Cave Biology (Biospeleology)] To popularize the field Biospeleology among other Biologists
• [https://web.archive.org/web/20190321215351/http://www.cavesofmalaysia.com/ Malaysian caves and limestone hills]