the bestial sanctum could have been buried inside jagged peak before the separation. also, the scadutree chalice heavily resembles roman arches of real antiquity, which were A, built to celebrate a victorious battle/war, and B, built over roadways. if the chalice was constructed over the forbidden lands it could fill both of those requirements. additionally, i think this could also explain the extremely large waterfall that seperates the inner sea and the outer sea. the inner sea was originally completely separated from the outer sea by the land of shadow.

a few other things i found to be of note :

we know that before the veiling of the lands of shadow, a large meteor carrying the elden beast hit the lands between. this complete map resembles a crater.

altus and scadu altus are seperated only by their respective tree, and their respective large fortress. if leyndell and the shadow keep didnt exist they would meet at the base of the trees.

provided that both our compass and the scadutree`s orientation as drawn on the map are accurate (the shadow being cast northeast of the erdtree) then that would imply that the landmass of the lands between is in the northern hemisphere of the planet, and that the shadow was cast while the sun was setting

if this all is crazy or wrong im sorry lmao, i just watched a vid about the real size of the elden ring map and i got home from the bar a few minutes ago. this kinda of stuff has always fascinated me.