Nether in the ground

This is very normal in the version 1.16.1

those are a new structure called the ruined portal🙂

https://minecraft.gamepedia.com/Ruined_Portal

Thank you for your report!
We're tracking this issue as MCPE-81330, so this ticket is being resolved and linked as a duplicate.

That ticket has already been resolved as working as intended, which means this is not considered a bug and won't be fixed. Please do not leave a comment on the linked ticket.

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