When you're exploring the land of Omar you will come across three Circles of Life, each guarded by a Skeleton Captain, they don't hurt much but they have a lot of hit points. You can't do anything at these circles yet though. Continue on until you find the entrance to level 21, where you will find another three circles, but again you can't do anything with them for the moment.

Go down into the dungeons, and on levels 21, 22 and 23, you will find a Offerings Room, all of which are guarded by three Skeletons Captains each, the same as the ones you fought at the Circles of Life. Once you kill them, down one end of the room will be a bunch of teleportation pads, and when you stand on the right one it will teleport you into the enclosed room at the other end, which contains a Flower of Shade. The right teleportation pad is the middle pad on one of the sides, except on level 23, where I believe it's the middle pad (I may be wrong there).

Once you have all three Flowers of Shade, return to the land of Omar and place the three flowers on the three circles just outside the dungeon entrance. They should disappear, and reappear in the Circles of Life as Flowers of Life. Take the Flowers of Life down to level 24 where you will find the Pyramids of Light, place one flower in each of the smaller pyramids, and that will open the large center pyramid, where you will find the Crystal of Integrity.