Find the Goddess Morrigan (in her crow form) south of the X-roads in Tara. Ask her Maze then ask her yes. Choose your difficulty level.
Morrigan's Maze is a randomly generated area that is different every time you go in.
This includes the rooms and layout that make up the area, but also the items that can drop.
There is a pre-defined pool of items that can drop in your particular instance of the maze, the stats on the items themselves are not randomized.
Each instance of Morrigan's Maze is split up into four areas. The first three areas have some trash mobs as well as a "boss" that appears after killing all of the trash mobs (the exception being the "vision of life" - you do not need to kill this mob for the boss to show up. In fact, if you do, you will die). The final area is just one boss.
The items in this pool are usually dropped from the "boss" at the end of each area, but have a small chance of dropping from the trash mobs as well.
The chance of gear and the chance of higher quality gear is determined by the difficulty of your instance, with higher difficulties resulting in a higher chance.
You can also obtain gear from the halfling in the third area by spending the crow coins you collect throughout the maze. Sometimes there is a quartlering down from the halfling that will allow you to gamble crow coins by giving him an amount of coins and then choosing 1 of 3 chests. If you choose correctly it will double your wager.
There is a random chance of finding an altar or a chest in the maze as well. Place 1 crow coin on the altar (no more than one) and it will transform into a random item - sometimes an ingredient and sometimes equipment. You can also put some of the items you have already looted on the altar and they may change to another item in the loot table. If you find the chest you can put crow coins in one at a time until you've deposited 10 crow coins and the chest will open. This is also a random item that will populate. Sometimes you win, sometimes you lose.
If you die in the maze you will be transported to Morrigan's room and your corpse will spawn for you to loot. You can then either ask Morrigan to "return" to the maze or "exit" if you've had enough.
Brigid's scroll: recite for census spell
hand of fate: use on a mob to insta-kill it
feather of the phoenix: use to cast firestorm on room
pearlescent white cross: use to cast bless and protection from evil