Nether or underworld

I have been letting my imagination run wild a bit and I have come up with an idea that has left me a bit obsessed, the idea of ​​an alternate map, type sea of ​​the underworld, that can be accessed from the original map, it will take a ritual key or something like that, and something similar will happen like when pirates return from the world of the dead in pirates of the caribbean the end of the world.