Royal Halberd Spear/Polearm

Inside Ulria Grotto East Cave.

Inside chest

Inside the Second Gatehouse.

Inside submerged metal chest near the waterfall.

You can grab it with Ultrahand, but you may need to create a platform near it (eg. with Ice Fruit).

Inside the Sanctum.

On the ground near the top of a ladder.

At the base of Hyrule Castle.

Inside chest hidden by breakable rocks.

On ground floor of watchtower at the west side of Hyrule Castle (base).

At the base of Hyrule Castle.

Inside chest atop one of the eastern watchtowers.

At the base of Hyrule Castle.

Inside chest at an emptied out river.