The dwarven minefield is a dangeorus yet lucrative special room located somewhere on GC 2-4.
The dungeon level the minefield is generated on can be easily recognised as it's larger than normal, with very large rooms and long corridors. The minefield itself is located in a massive room with many mines, both active and inactive, and some backpacks of gunpowder scattered around. Luckily, you can rather easily get the belt of levitation before entering the minefield and with it you don't need to worry about blowing yourself up. The room has plenty of valuable loot, so explore it throughoutly.
If for some reason you do not have the belt, you can use a ring of searching instead. This will slow your progress through the room massively, but you should still be safe enough doing so. Before taking each step, search eight times with the ring equipped. This should reveal all mines or traps around you. Without the ring, you can still attempt to explore the room by searching around sixteen times before each step. Doing so obviously requires a large deal of patience, but the consequences of stepping on a mine in the minefield are often lethal - any explosion will set off a chain of other mines and backpacks exploding in your face.
If you don't feel safe enough, feel free to skip the minefield and return later. You could also pray to Silva to cause all mines on the level to explode, but this risks breaking useful potions and burning scrolls.