Going by the standard definition, Sanctuary is a sacred place often a haven (a place of safety).
Sanctuary can be grouped into two forms
The Religious sanctuary and the Other form.
The Religious Sanctuary; is usually a religious building where religious people come to worship and seek the face of God. It can be a church, mosque, or shrine. And it's regarded as a sacred holy land, as worshipers take their burdens there and feel safe because they are in the presence of God.
The Other Form; This may be classified as Human sanctuary by others but I prefer to use the words the other Form because not just humans need sanctuary, animals also do need one. An animal sanctuary is a place where it feels safe and at home. Most animals are been taken from their natural habitat to live somewhere else, for example, some water bodies live longer in their natural habitat(river and sea) than in an aquarium because to them their natural habitat is a safe heaven.
For humans, sanctuary can either be a place or a person
It can be a place where they can meditate, draw inspiration and feel safe. A writer needs a quiet environment to stay focused to give his/her best work and that's his sanctuary.
It can also be a person they draw inspiration from or someone that guides them in life at a point where they feel lost and don't know what to do.
In Conclusion;
Sanctuary is a place of purity where safety can't be compromised and rest is assured.
