By "Stone Protection Tower", I mean vault.
So; Vaults are typically the most dangerous thing an adventurer will conquer, yes? There is no major movement challenge; only combat-based. Plus, I doubt the demon would simply let the hero go after they get the slab. So, I propose an idea.
When the slab is gotten, the Vault will start to destroy itself in a last-ditch attempt to keep you from escaping with the knowledge of the demon's true name. By "Destroy Itself", I mean the slade will begin to crumble into a heavy, brittle rocks, straight from the walls and ceiling. Stones will fall from the ceiling, and worst of all;
The door will 'melt' away, keeping you trapped.
This is you and the vault's last dance. As the structure crumbles with you inside, your goal is to find an escape - any escape - before you are crushed alive. Some examples of possible escapes include;
- Jumping through openings created by the crumbling walls
- Climbing through the ceiling once the highest layer starts to crumble
- Surviving inside until the building collapses to the point where you can walk out
- Breaking through the now-brittle slade; which is, while difficult, now actually possible with enough skill
And the demon would probably have some method of actually knowing about this, due to it being so important. So, if the demon's civilization is around, expect a large goblin army to be marching toward the vault"s position.
Please tell me what you think of this idea!