If you are talking about a visor on a helmet or hat:
* No visor - This is the most straightforward antonym.
* Brim - If referring to a hat, a brim is the opposite of a visor.
* Open face - This is used for helmets that lack a visor.
If you are talking about a visor on a car:
* Sunroof - This offers a panoramic view, the opposite of a limited view through a visor.
* Open top - This refers to vehicles without any roof at all.
If you are using "visor" figuratively to mean a "shield":
* Exposure - This means being open and vulnerable, the opposite of being shielded.
* Vulnerability - This is another word for being exposed to danger.
The best antonym for "visor" will depend on the specific context and meaning you are trying to convey.