Ex-Nightwish frontwoman Tarja Turunen played the Wacken Metal Church stage, as well as the Black Stage, at the 2016 Wacken Open Air Festival in Germany. Turunen's performance on the Wacken Metal Church saw the singer perform covers of Slipknot's "Vermillion, Pt. 2" and Rammstein's "Ohne Dich," as well as a few other songs, accompanied by strings and a piano.
You can check out the two covers below (both timestamped), which are just beautifully done.
Here's Slipknot:
Here's Rammstein: