Quote: " Breaking apart pallets (enough for a project this size) is in a PITA and I don't want to do it again."
There is a trick to that, but I will keep that a trade secret since you don't want to use pallets anyway.
You could do a round house too if you want something different. (no corners for the evil spirits)
Just drive a stake in the ground at center, and tie a string on it, then use that for the radius to lay our your circumference of the circle.
Chord wood works well for that if you don't want to use stone.
Or, you could even use cob and make a round door to make a Hobbit house.
A tapered wall on the front could give the illusion of the hill, and any type of ivy could be used to cover the roof for the ground roof illusion.
That way you could get a similar look of a hobbit house without digging in a hillside or using sod for the roof.
Just a thought, but everyone loves hobbit houses.
Oh, and don't forget about A-Frames, because they are easy and quick to build.
I like the castle Idea, but I would make an arch for the door, and make tiny windows, to give the illusion of a 2 or 3 story structure with a draw bridge door, so it would look more like a real castle from a distance.

Coding things my way since 1981 -- Currently using AppGameKit V2 Tier 1