The spiritual world is the greater reality beyond the limited material world of our experience. This world is made of temporary matter, but the permanent, spiritual world is made of spirit, which is the essence of all life. The spiritual world is also known as Vaikuntha, the place of no anxiety, where there's no death, disease, or enmity. Life is harmonious because everyone has a common purpose—transcendental, loving service to the Supreme Person.
The Supreme Person has unlimited energies, both spiritual and material. The spiritual world is made completely of His spiritual energy, which is characterized by complete happiness, full consciousness, and permanence. He lives on each Vaikuntha planet, either in His original form as Krishna or in a Vishnu form. The innumerable Vaikuntha planets are all self-luminous, and beautiful beyond our imagination.
(Image is a painting of the Vaikuntha planets in the spiritual world, based on descriptions found in the Srimad-Bhagavatam.)