神秘而壮观的洞穴
原网址：>>https://static1.squarespace.com/static/564177d6e4b083e275d816fd/5a2eff314192022b9fc7141d/5a27d0f88165f5ccfe67bc39/1518008765702/DSC00960.jpg?format=2500w
>>https://i0.wp.com/www.cityoftheweek.net/wp-content/uploads/2017/04/how-to-visit-benagil-cave-portugal-11.jpg?fit=1200%2C900&ssl=1
>>https://www.flickr.com/photos/96657819@N07/10657387665
原网址:https://commons.wikimedia.org/wiki/File:Goats_Hair_Caves_on_Gibraltar_and_sunlight.jpg
<<https://lamagiadicefalonia.com/wp-content/uploads/2017/03/lago_melissani.jpg
<<http://www.dronestagr.am/wp-content/uploads/2017/11/DJI_0085-Edit-2-Edit-1200x800.jpg
<<http://mybestplace.com/aroundtheworld/wp-content/uploads/2016/06/Melissani-Cave-Kefalonia-Greece-IMG-2-TESTO.jpg
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奈卡水晶洞（西班牙語：Cueva de los Cristales），是「世界上最大的地下水晶洞穴」，洞穴內晶體為石膏而非水晶，位於墨西哥奇瓦瓦沙漠奈卡山脈一帶，知名為「奈卡任務」的一組科學家積極參與研究這些洞穴，在這悶熱潮濕的環境中，人類在裡面活動超過10分鐘會有生命危險，需要穿有高科技冷卻功能的防護衣，才能進入洞穴裡
source: https://twistedsifter.com/2015/11/cave-of-crystal-giants-naica-mexico/
奈卡山脈是由火山活動而形成，一直沉沒在50℃以上礦物質豐富的水中，奈卡的結晶其實是一種稱為亞硒酸鹽（Selenite）的石膏結晶。
原网址>>https://l43.cdn-news30.it/blobs/variants/2/9/4/5/29453e94-35c5-406c-bf7f-a83c140a9cab_large.jpg?_636151827000549812
原网址：flirKr
奈特柏德洞穴(Nettlebed Cave)深889米
原网址：http://www.geologyin.com/2016/12/inside-nettlebed-cave-crystals-in-pool.html
>>https://www.thousandwonders.net/Gunung+Mulu+National+Park
>>https://www.bikeandtours.com/application/files/7215/2264/3741/Mulu_National_Park.jpg
>>https://a.travel-assets.com/findyours-php/viewfinder/images/res40/53000/53496-Gunung-Mulu-National-Park.jpg
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>>http://farm9.staticflickr.com/8202/8168992790_16b9ba0875.jpg
>>https://cphtravel.com.my/wp-content/uploads/2018/10/Bau-fairy-and-wind-caves-800W.jpg
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