how to manually make a voxel terrain?

ok so im trying to make a fps game in voxel stile and i got stuck doing the terrain of the game, because i want it to be in voxels like minecraft but not procedurally generated, but all the tutorials that i find are about doing procedural generated terrains, any one knows a solution?
Also i don’t need it to be breakable

you can use the remesh modifier in blender to achieve this effect. check out this blender tutorial.