I made a sand castle on Tinkercad and its a mold. I'm a beginner so I hoped you liked it.

The pictures show the mold before the modifications (first .stl file.)

I made my Sand Castle from making a real sandcastle in mind by putting geometric shapes and it didn't turn out as expected but it still looked cool.
The second file I made some changes the change I made was I got rid of the 2 walls that were separating 2 blocks from the whole model

3D printing:
Change dimension, Scale to 50%, Layer height to 0.30mm, In fill 5%, Number of shells 2, Raft is on Supports off, Material Makerbot PLA, Extruder temp 215c.