Some people who pass through this type of portal will see it as a physical door that opens and closes. Others may view it as an arch that suddently becomes transparent. Others may see it a fibrous cloth, with a type of zipper or method to divide it, almost as if it is a type of "tear" or opening to allow them to pass. Some may see it as a narrow tunnel, and still others view it as kind of a cloud that suddenly becomes clear as they walk through the mist. How the portal to another dimension presents itself to you is often based on what your mind will accept for this new reality as well as the location of where it is mapped to. The important thing to know is this visualization of the portal is the way your mind now becomes ready to accept your transition from taking you from one point of reality into another point of reality. With this step, your energetic self is now poised to accept information, remember it, and transfer these new messages to your physical self.
Should you be hesitant to go through a portal, you may wish to visualize having a cord, rope, or string attached to you and secured on your side of the portal. This way you have a mental image (and method) of finding your way back home to your current reality. This should help you reduce your fears or hesitation to explore what is beyond.
In addition, once you pass through the door, if you find yourself uncomfotable in this new reality, you can usually return just by mentally wanting to return. Thinking thoughts of going home and returning, or forcing yourself to "wake up" or "end the meditation" allows the experience to quickly end. Your spiritual energetic self quickly will return to "your side" of the portal.
If you are in a rush and quickly and return back home, most likely you will FEEL a bit stunned for a few seconds until your spiritual energetic body readjusts to your normal reality. You will probably feel a type of "vibration" and perhaps a bit of dizziness until you normalize. This only lasts a few seconds and no need for alarm; it is only temporary.
The experience of passing through a portal and visiting other realities is one of the wonders of the Qi cultivation process. There are many different types of energetic travel experiences, and passing thorugh a portal to a new dimension is just one of the methods where a person energetically travels to other realities.