Before there was humanity and Grimm, there were giant beasts created by the God of Light to stop any outside forces from destroying or using the planet for their own will, and the beasts were called kaijus, and are given names and locations as followed:

Godzilla, King of the Monsters and the God of Destruction: Ocean near Vale

Mothra, Queen of the Monsters: Landmass north of Sanus

Rodan, the Fire Demon and the One Born of Fire: (possible) in a volcano on the same landmass as Mothra

Anguirus, the Fierce Dragon and Godzilla's Companion: Deep in Lake Matsu

King Caesar, Legendary Monster: Deep under Mountain Glenn

MUTO(male and female): Unknown

There are only a few who know's about them: Ozpin/Oscar, Salem(I guess you can count them?), the God brothers, Grimm(I guess?)