I’ve ran into this a few times, and I’m not sure how to get in besides getting lucky with a scroll of teleportation. Maybe Etheral Chains, but there’s nothing for them to hook onto.
I’ve checked the walls everywhere in the vicinity, and I can’t find a hidden door.
Others have already mentioned to burn it, but a wand of disintegration works as well.
You mentioned the chains, and if you use them on the space right before the far wall, it will pull you in the room. I wouldmt recommend it though as you may not be able to get out before you starve.
Just make sure you have enough charges