Board Thread:Lore Discussion/@comment-25958616-20151001211714/@comment-91.96.221.210-20151002153325

Yup, they are most likely guarding the Lost Sinner... For his/her own safety, I assume. Lost Sinner is probably the prince or princess whom the whole Belfry story is about. Probably lit a fraction of the first flame, created life, meaning those Belfry dwarfs, something went wrong and he/she imprisoned him/herself. It's basically the Witch of Izalith's story retold.

The Lost Bastille was made by the Old Iron King, evidenced by the door. I would assume he sent a Flexile Sentry there, though this is SotfS only, so canon is questionable. I guess he sent that thing there to make sure Sinner stays there... Probably aware of that certain lord soul which could bring his kingdom down... Turned out, he was his own worst enemy, though!