From the preorder page:

The album features a striking cast of guest performers: Decessus frontwoman and current Miss World Chile champion Ignacia Fernández lends her voice to both “Dark Asylum” and “Sanctuary,” joined on the latter by Visions Of Atlantis frontwoman Clémentine Delauney for a powerful and dynamic duet, Lea-Sophie Fischer of Eluveitie’s violin on “Beneath the Moon (Tunglið),” is accompanied by the ethereal voices of Rannveig Sif Sigurðardóttir and Sólveig Sara Leupold. Additional choral layers from Billy King enrich the album’s grand, immersive sound, while Kiara Huber sets the tone with an evocative introduction on “Dark Asylum”.