Trouble creating a volume from a plane My friend and I are trying to create a landmass for a nautical table top game. We want to create an STL file to 3d print. The piece is seaside village on a hill at the edge of the board.
This being my first blender project I sculpted the land from a plane and then added the buildings as cubes. Now I want to cut the edges of the landmass to be flat and filled in, and I am have a lot of trouble.
The first image is the model. The second image represents where I would like flat faces for the STL. These are cubes added for the purpose of a Boolean difference.
I have tried a couple of things.

Cutting the plane and manually filling all the vertices. Was impossible to get all vertices filled.
Extruding the edges down and then filling to bottom before trying a Boolean difference with cubes on the bottom and back (see the second image). Blender had a meltdown with the landmass disappearing entirely but the buildings remained (not sure why since they were already joined as the same object).

Please let me know if you have any thoughts.
Thanks!
It's not working properly because you simply joined the two cubes. Now they are a single object, but in Edit Mode still two separate meshes with their own volume, but overlapping in some parts.
In order for the Boolean Modifier to work, the volumes you want to subtract from the landscape have to be either separate without overlapping or you have to create one continous volume for the overlapping cubes.
Since the overlapping is necessary in your case, you have three options, all require you to separate the cubes beforehand and make them two objects again:

Work destructively by first subtracting one cube, apply the modifier and subtract the second cube.

or:

Give the first cube a Boolean Modifier and join it with the second cube by setting it to Union, then choose the first cube for Difference in the Boolean Modifier on the landscape.

or:

Maybe the simplest way: put two Boolean Mdifiers on the landscape, choose one cube for the first modifier and the other cube for the second modifier.