How to melt an ice cave
Installing a door to keep heat out of an ice cave does just the opposite

ICE PALACE Frigid winter breezes serve as natural air conditioning for ice caves such as the Ningwu ice cave in China’s Shanxi province, new research finds. Caves sealed by airtight doors block circulation and could melt within decades, the researchers warn.
© Wang Shen/Xinhua Press/Corbis