Located a short walk east from Brimestone is the famed Megamaze. This massive underground maze is a true maze, with no 'trick rooms', so it can be easily, if tediously, mapped. Designed by Sphynx, one of Mystic's long lost implementors, this area is a perfect square measuring 27 by 27 rooms for a total of 729 rooms, making it one of the largest in the game (the road system is it's only rival, and I do not feel like counting the road spaces to determine which is larger). Characters between levels 30 and 45 will find this area a good place to gain experience, due to the relativly large number of mobs.
Few mobs in the Megamaze are aggressive, but those that are can see you even if you are invisible, so use caution when low on hit points. The entire maze is a no-recall zone, so be sure and bring along an emergency potion for when you get lost (trust me, it will happen).
There are a few useful items to be found in the Megamaze. These include Snake Earrings, Home-made Sleeves, and Magic Lens.