"Gotterdammerung" is the last in Richard Wagner's cycle of four operas titled "Der Ring des Nibelungen" ("The Ring of the Nibelung").
The title is a translation into German of the old norse phrase "Ragnarok", which in Norse mythology refers to a prophesied war among various beings and gods that ultimately results in the burning, immersion in water, and renewal of the world. I find this music very soothing for my nerves.