Three Lower Realms

The three lower realms of the six realms

Four types of hell beings:.

1) Beings in the Great Hells.

There are eights types of existences in the Great Hells.
1.1) Reviving Hell
1.2) Black Line Hell
1.3) Mass Destruction Hell
1.4) Wailing Hell
1.5) Loud Wailing Hell
1.6) Hot Hell
1.7) Intensely Hot Hell
1.8) Unceasing Torment Hell

2) Beings in the Surrounding Hells

Around each of the eight Great Hells are the following Surrounding Hells.
2.1) Pit of Fiery Embers
2.2) The Putrid Swamp
2.3) The Razor-filled Path
2.4) The Forest of Sword-leaf Trees
2.5) The Shalmali Tree
2.6) The Burning-liquid River

3) Beings in the Cold Hells.

Existences in the Cold Hells are of eight types:
3.1) Blistering Hell
3.2) Bursting Blister Hell
3.3) Chattering Teeth Hell
3.4) Exclamation of Cold Hell
3.5) Moaning Hell
3.6) Cracking like an Upala Hell
3.7) Cracking like a Lotus Hell
3.8) Great Cracking like a Lotus Hell.

4) Beings in the Occasional Hells.

The Occasional Hells are suffering situations that are sometimes experienced in the human realm. These situations resemble a hell realm, for example being consumed by volcanic fires or frozen in ice. Those caught in car accidents, in which the cars burst into flames, experience suffering similar to the beings in the Wailing Hell. Beings crushed in a earthquake experience suffering similar to the Mass Destruction Hell. During wars there are many environments that could considered Occasional Hells. They are called Occasional Hells because the environments do not remain as hell forever, but may change according to a person's karma. (#4)

B) Hungry Ghost Realm.

The cause of rebirth here: Very misery.

There are six kinds of suffering that hungry ghosts experiences:
1. Intense heat.
2. Intense cold.
3. Intense hunger.
4. Intense thirst.
5. Great fatigue.
6. Great fear.

Note: hungry ghosts have greater mental capacity than animals. Some are very powerful, some can see the future, some even have miracle powers and contaminated clairvoyance with which they help or harm human beings, and some can understand dharma if it is explained to them. However they all have greater degree of suffering than animals. Hungry ghosts can see human food from a distance, but when they approach it is disappears and they have to experience the anguish of disappointment. The only way that they can actually obtain human food is by its being especially dedicated for them. While they search for food they experience constant anxiety, fearing that any food or drink they see will be snatched away from them before they can lay hold of it. see also (#2)

C. Animal realms.

The cause of reborn here: abandoning the Dharma, being disrespectful to the Dharma and its propounder, or criticising other spiritual practitioners. (#3)

The five general suffering:
1.Suffering from being eaten by each other.
2. Suffering from being stupid and ignorant.
3 Suffering from being hot and cold
4. Suffering from being hungry and thirsty.
5. Suffering from being exploited for work.


References:
#2: Liberation in the palm of your hand. page. 338-345.
#3. Path to Enlightenment in Tibetan Buddhism. page 269.
#4. Path to Enligtenment in Tibetan Buddhism. page 258-265.