This crazy seed is -3929498278129529376 . I was playing a normal Survival mode in a random seed and very lucky saw 2 Ancient City under a big snowy mountain . I had learn about under a mountain that y = bigger 100 will got a change has an Ancient City . I think this isn't 1 mountain only , so it has 2 Ancient City

Youtube : youtu.be/I50SVqp0AKw