Instructions
Inspect the local and region view windows of the site selector when choosing a site to start a fortress. Volcanoes and magma pipes are visible in the local view window and are represented as red "≈" tiles while the region view window represents volcanoes and magma pipes as red "^" tiles.
Look around your fortress location with the arrow keys when you embark to a fortress site and change your z-level with the "<" and ">" keys. Volcanoes are always visible on embark, but magma pipes may not be immediately visible if they do not reach to the surface. You will have to find and penetrate the magma pipe If the magma pipe is not visible.
Divide your fortress site into 64-tile sections starting with the upper-left corner. Each tile in the local view window of the site selector represents 64 tiles in-game. Locate the fortress section that contains the magma pipe as positioned in the site selector and dig a down staircase in the center of that 64-tile section. Dig up-down stairs in a column under the down staircase until you find the magma pipe.
Dig to find magma pipes near your fortress. Your miners will automatically stop digging if they detect the warm stone in the two to three stone tiles around a magma tile. Dig around the warm stone to determine the magma pipe's dimensions, then dig a down staircase or a channel in a tile above the center of the magma pipe.
Dig to the magma sea at the bottom of your fortress map if all else fails. The magma sea is found below the last cavern level of your fortress site and can be found anywhere from 5 to 450 z-layers under the surface. Once you have found the magma sea, you can build a tower of screw pumps, known as a "pump stack," or a magma piston to pump the magma to your fortress for use.