Cavechat.org

'Tis a nice article on CJ-3 Cave in Spain, but as it shows, it can be a deadly cave. This reminded me of the mother lode area of northern California, where a high concentration of CO2 is found at certain times of the year. A lack of the right breathing elements, like in CJ-3 are to be respected, as those in California.

http://elpais.com/elpais/2017/01/02/ine ... 76581.html