Realm Of The Living
This is the realm in which you will begin gameplay - alive essentially. Whilst you remain in the Realm of the Living you will be able to see the spectral forms of enemies in the background but they will not harm you and you will be unable to kill them. When you are killed the first time, you will enter the Realm of the Dead.
Whilst in the Realm of the Undead, if you can locate a Wicca Room then you can return to the Realm of the Living. There are differences between the two Realms which make moving between them necessary to find all the secrets and unlockables in the game.