* Tunnels can not be opened if the north-west corner is more than 4 dirts below [[Water#Water level|water level]].
* You cannot [[Mining#Surface_mining|surface mine]] to correct an oddly shaped entrance once it is open. So you must make sure to have the tile in the exact shape you want it to be before you open the mine.
* The maximum height of a tunnel entrance is 270 slope, but you would not be able to continue mining because of ceiling height restrictions. Tunnel slopes should be less than 235.
* The maximum height of an tunnel entrance is 90 slope if you plan to add a mine door.
* You may create a mine entrance up to 3 tiles wide.