Listening to several
Van Canto songs. They call themselves "metal a cappella", and that's sorta true, because the only actual instrument are the drums; all other instruments are made by human voices, besides the lead singers.
These are a few of their own songs; they also play covers of other metal bands, I'll post some later.
Magic Taborea
https://www.youtube.com/watch?v=pYdoFtPtFKU
Lost Forever
https://www.youtube.com/watch?v=kJ0n-1FmFiw
Last Night Of The Kings (sounds a lot like Blind Guardian's "The Bard's Song")
https://www.youtube.com/watch?v=rt4CQc1MSso