Arthur went down into the underworld all right, but it was just the realm of the dead, not a place of eternal punishment, and therefore not hell.
Anwen (with the -wen showing it's feminine, not the masculine -wyn) is in the database here. I taught an Annwen once, who grew up in a non-Welsh working-class neighbourhood and in self-defence called herself Anne.It is beautiful ... I called her Annwen when nobody was listening!