When you think sand molds, you think castles. When I think about castles, I think about the famous castle city from The Lord of the Rings.
It's layered layout should work great in making the sandy negative, and if anything breaks of it is “Minas Tirith, besieged”.
For Gondor!
Just printed it for tests, and I think its a bit small, so maybe print it at 200%.
The author marked this model as their own original creation.