“But what is reality?” this is the incipit of short story by Stanley g. Weinbaum published in 1935. We can define this short science fiction story as the first on virtual reality. The main character uses spectacles to enter a vvirtual world, a different world which inhabitants also live a different reality.
The short story is available for free on project gutemberg
On YouTube I found an audiobook version
I found also this interesting essay on the potential of present technology related to the immaginary world by Weinbaum