Heaven is opposite dimension, when compered to Underworld. Heaven is world, where everyone wants after their death. Unfortunately, you don't get to there, if you die. Maybe you have a mission? But, you can get to Heaven with portals. To create portal to Heaven, you need 1 Goodness altar and 5 Goodness bricks. Heaven is usually a good place to be death, but now its corrupted with machines. Maybe you can help them somehow?
Mobs found from HeavenEdit
Ther's many creatures found from Heaven. Some of them are good, and they want to help you, but some of them are evil, souless machines. You have to identify friends and enemyes.