Somewhere in the land of Omar you will find The Gate of the Damned, guarded by a spectre who doesn't want to let you pass. Talk to him twice and he will attack you, and upon his death he will drop a key. Take this key and enter The Gate of the Damned (entrance to level 21), then on level 21 you will find a room with a locked door, use the key you got from the spectre and you will find the room is full of spikes coming out of the ground. You have to time this right so that you can run across when the spikes are down, or just take a couple of healing potions and not worry about them, and at the end of the room you will find The Cross of Crime. Take this and then go around to the back of the table, and there's a teleportation pad there to save you going back over the spikes.

Now continue down to level 22 where you will find a similar room to the last one, but with a different pattern of spikes, do much the same as you did last time, except there's no teleportation pad to get you back out again, so you will have to make 2 trips across this field of spikes. Once you have the Cross of Penitence, go to level 23 and do the same for the room you find there, this time for the Cross of Pardon.

Then continue down to level 24 where you will find a square room with bars on each side, and on one side there will be a switch which opens one of the gates. Go in and give the spectre imprisoned there the three crosses, and then he will attack you to get you to kill him and offer him the salvation of death. He will leave you the Crystal of Integrity on his body as your reward.