From Matt Yglesias comes an interesting website on Pyongyang's subway system. While the public system seems relatively small (only 17 stations), there are indications that the secret military subway system is far larger:

The extent of the secret system can be guessed by the number
of trains purchased from Changchun, more than twice the minimum number
needed to run the public Metro system. (See Trains.)
Even allowing for spares, and extra capacity for more frequent service,
the indications point to a system that may be larger than the two lines
known to exist.

Just as interesting was the disclaimer that Simon Bone, the website's owner felt obliged to put on the subway music page:
Please note that although these are propaganda songs, and North Korea is not generally a signatory to international intellectual-property conventions, these materials should be used for private, non-commercial, informational purposes only. By downloading these files, you agree to delete them from your hard drive and any other storage devices within 24 hours.

Somehow I imagine that in the unlikely event that the North Korean government decided to take action against someone sharing their music, it would not take the form of a cease-and-desist notification. For those who want their fill of North Korean martial music without the fear of being kidnapped and sent to a labor camp, the official North Korean website offers the Korean Friendship Association's hymn, "Song of National Defence."