There are several different planes of existence some are more well known than others not that any are easy to get to and back alive.
Material Plane Edit
The material plane is the plane that is well known and that the mortals walk.
Astral Plane Edit
The Astral Plane is the inbetween of the Fire lake plane and the celestial plane this is the place you go when you first die and wait to be moved, sometimes ghost never move on from this plan haunting those on the material plane. This plane is the easiest to go back and forth as its side by side with the Material plane.
Fire lake Plane Edit
This is the plane were demons and devils live this plane is made up of seven layers each one ruled and named after one of the seven deadly sins: Lust, Gluttony, Greed, Sloth, Pride, Envy, Wrath. Each layers ruler obeying Wrath the ruler of the seventh and last layer. Going across all the layers of the Fire lake Plane is a dark river, the only way to travel the river is by skeleton gondola.
Celestial Plane Edit
This plane is filled with angels and celestials it's also said to be home to many of the gods. Some races believe that when you die you come to this plane. It's said to look like a white kingdom.
This plane is said to be a void of nothing a blank space in time and only the most unnatural and monstress creatures live, nothing but these creatures called Slaads can live here. Over time many have tried to come here but all have failed.
Elemental Plane Edit
This plane holds and is home to all kinds and types of Elementals. These Elementals are summoned from this plane to the Material one often making it quite easy to get to. There are four pocket planes around this one they are: Air, Fire, Earth and Water these pocket planes feed into the Elemental Plane.