*If there are two lower corners identified then the opposite border will be the top of your mine opening and will be completely flat as well, leveled at lower corner of the opposite border.
*'''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.
*When tunelingtunneling, entrance tile is limited by reinforced cave floor as any others (requires that all four corner of the entrance tile not be also one of a reinforced tile). So, when you are tunneling an entrance from the outside and receive the message, {{event|inline|The ground sounds strangely hollow and brittle. You have to abandon the mining operation.}}, you most likely have a reinforced floor inside the tunnel you are trying to open. Enter the mine from another angle and remove the reinforced floor.*Tunel Tunnel from outside will ever make a downgoing entrance 20 slope or more, even if there is a flat cave inside. Tunnel out from inside will only remove the rock walls without changing the ground level.
*To correct that entry slope you can further raise the mine corner floor with concrete but if ground reach is deep underwater. If you don't want any ugly water on the floor in the mine, ensure that both lower corners of the entrance are at least at height 28 (hover the corner with the mouse).
*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, after 51 actions. A stone shard or two later, and an entrance will be created.