Celtic metal is a sub-genre of black metal. Its focus is on Celtic mythology and instruments mixed with black metal. Celtic metal has developed a huge underground scene in Ireland, where pioneers like Cruachan, Geasa, Waylander and other such bands play. By far the most successful album is Cruachan's Tuatha Na Gael which sold out its label's supplies within a few months. It cannot be considered a great success, however, because it was a small label and only pressed a few thousand CDs.
Although still a sub-genre by itself, Celtic Metal has already spawned a few mixtures and sub-genres.