This is my method for making a flat mine entrance, which I learned from Lolth.

• Improved Compass is beneficial to see height.
• The ability to cast the Strongwall spell (70 faith, 70 favor, 70 difficulty).
• Magic mushrooms or some veggies and an altar to sac.

1. Have a plan in place.
2. Adjust your entrance tile so it is significantly vertical and flat for an entrance. I use 33 as my entrance tile height (vertically between low corners and high corners) since the first floor of a building is 33 slope.
3. Tunnel in, which creates an entrance 20 slope down.
4. Mine up to open the second tile in which creates 20 slope up.
5. Mine in straight to open the third tile which creates a flat in line with the entrance.
6. Turn around and Strongwall the floor of the entrance tile (inside) and the floor of the second tile.
7. Standing on the third flat tile, mine outward the second and first tiles to create the flat entrance.

If you need help let me (Freth) know.