Everything is made up of energy. The floor, the furniture, the air, even you are energy. The cells that make up your body are energy on the most minute level. If you could see into this hidden world you would see that matter no longer exists. That the only thing that holds one molecule to another is the attractive force between them. And if you go even deeper into what makes up molecules into the world of quantum physics, time and space collapse and do not even exist.
The Crystal Palace is located between the Sephira Malkuth and Yesod, at the "Universe" Tarot Card location. Technically the Crystal Palace is part of Malkuth, even though it is located on the crossway. As such, this place is one of the easier places to reach using your favorite nonphysical travel method. Usually you enter a crystal cave first before you reach the palace. But you may find yourself in either place.
The Crystal Palace/Cave is where you go to learn that you are made up of energy and that your form is changagble. You think you are locked into your current form and there is no changing it. You are wrong. This assumption that your form is unchangeable must be let go of, if you are to understand the higher spiritual concepts that are yet to be learned. Here in the Crystal Palace/Cave you can experience your form as a changeable thing. It is also a good place to learn about energy and how energy can be controlled by your will to suit your current needs.
The main contact inside the Crystal Palace is a short man who calls himself the "Crystal Keeper." You may see him or meet him while there. He may give you the quest you need to accomplish and or your gift. The primary one-time gift here is a significant upgrade in spiritual energy. Your spiritual energy bank is enlarged so that you can contain larger more complex spiritual experiences. It also means you will have more spiritual energy to go around in your daily life. You will need to complete some task, first, before you will be given this spiritual energy boost. These tasks vary but often center around the theme that you are energy and you can reform that energy to your will.
Secondary gifts here are often crystals that contain some knowledge for you to assimilate. Some crystals can bestow on you unusual abilities too, like past life recall, or invisibility. The cloak of invisibility is something that is often obtained here.