Snake mentioned by Dorry/Brogy & also seen drawn by Moon People in Enel's Cover Story
It's basically World Serpent, inspired from Norse Mythology obviously
While Land of Gods mentioned by WB is World Tree (Destroyed)
Ancient Kingdom is related to both, with a Piece of it still existing inside that World Dragon
All Three represent Major Kingdoms of The World with each being Original Home of Samurai (Ancient Kingdom), Giants (World Dragon) and
Celestial Dragons or at least who they Worship (Land of Gods)
Ancient Kingdom Original Name is "Ryuo Kingdom" or basically Kingdom of Flowing Sakura. World Snake's Name is "Mantra" while Land of Gods was given a Name related to Haoshoku Haki, but it's Exclusive to Mary Geoise similar to how Wano call CoA as Ryuo (Not revealed yet but maybe Hinted at somewhere)