modify terrain by player

it is possible left the player modify the terrain, like in Sims, and maybe dig a hole?

You answered someones question who had the same question as you, and i posted a link on his page. Ill give you the same one:

modifying terrain height under character

If you want to make holes, I suggest you get a voxel package. There are several in the Asset Store, some are even free. I’ve used VoxelForm, it rocks. Well documented code with lots of samples.