The ??? is a Hardmode Lore item found in chests in The Void. It can be read by left-clicking it while the Traveller's Journal is in the player's inventory, and can be accessed in the Codexes section in the Traveller's Journal.
This place... This place has been growing from me all this time.
The horror... The horror...
I want to pray to be eased from that sight. That sight has etched itself into my mind like the most invasive of times. And the worse thing... It is personal. My last overseers around volunteered to go with me into the dimension, and true enough they were terrified and filled with dread. But they could snap themselves out of it... at least for the moment.
Me? I can't. I can't make it. I'm not sure how long I can last. My dreams are getting more horrifying. The Worm is now moving around some kind of brain. The brain speaks to me in a familiar voice. I can't quite recognize it, but I know I had heard of it before. Around a time when bro was still around.
Please, grant me strength.