Each tunneling action has a chance to create a [[stone shards|stone shard]]. After a number of [[stone shards]] are created, usually 9, the message {{event|inline|You will soon create an entrance}} will appear. A stone shard or two later, and an entrance will be created.
* The two lowest slopes of your tile will form the bottom tile border of your opening, which will be completely flat. The top of your mine opening will be completely flat as well.
* 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.