Digging deeper, in the Granite State, would be frustrating. (Lots of huge granite boulders.)
Instead, earth will be piled up to create a hill. Under that hill, will be a hole.
does that mean we all have to build our own real hobbit Holes?
Only if you want the advantages: 1) low heating and cooling bills 2) low property taxes 3) less disturbed wilderness
There is no NH income tax. So minimizing property taxes lets you keep more of your money.
Do wizards bring fireworks if you are in a HH?