Can anyone explain the significance of this cross from St. Peter's Basilica?

[Notker23]

I had the opportunity to visit St. Peter’s Basilica recently, and I noticed this large cross in the back, I believe it was near the entrance:

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I assume the black square at the bottom is where there used to be a plaque explaining something about it. It just piqued my curiosity since it seems so plain and modern in the baroque splendor of St. Peter’s, and I was wondering if anyone knew anything about it.

 

[BoomerangToo]

It’s the sealed Holy Door, which is unsealed before each Jubilee.

 

[Roseeurekacross]

It was last opened in the year of mercy in 2016

 

[Notker23]

Thank you! That explains why it seems so plain, it’s just a temporary wall sealing a door.