The Centre of the Underworld

From under-fortress ancient
And spawning pit yet young,
From ship upon a sunken sea
And hollow crypt, they come:

The orc before a surface door,
The elf of deep below,
The thing erased from ancient lore
Are all compelled to go.

Through secret passage shallow
Or smoky fissure deep,
Dwarf-road long in ruins,
Or calcite cave, they creep.

An open cavern mile.
A dome of cut black stone.
A sea of blood-red tile.
A ready, leaden throne.