Umbrtka is a metal band from Plzeň, Czech Republic. They describe their style as "gray labour metal" although they admit their music has some black metal attributes, though the lyrics have nothing to do with usual BM subjects. Umbrtka sings about industry, work, manual labour, trains, factories and - of course - about Umbrtka himself, a real person who used to work in Plzeň's shredding facility.
Umrbtka is formed by four musicians - Morbivod (also Trollech, Stíny plamenů, War for War), Strastinen, Well and Karl. They never perform live, however manage to release two full albums per year.
Discography:

Zašpinit slunce (Make the Sun dirty) - 2000
Dělnický a bezdomovecký šedý metal (Labour and homeless gray metal) - 2001
Kladivo pracuje na 110% (The hammer works at 110%) - 2001
Kovostroj plzeňských pánů práce (The metalmachine of Plzeň's labourlords) - 2001
Hymny šedé síly (Gray force hymns) - 2002
Ozvěny špíny (Echoes of dirt) -2002
Betonová opona (The concrete curtain) - 2002
Nad propastí dne (Over the abbys of the day) - 2003
Melša - Frank Zappa meets Darkthrone - 2003
The Hand of Nothighness - 2003
Paměti špinavé lávky (Memorie of the dirty footbridge) - 2005
Lití podzimního asfaltu (Casting autumn asphalt) - 2005