From Fallen London Wiki
The pleasant dreams are of the Royal Beth, of course.
The unpleasant dreams are not. They're of the Neath itself.
It's a vast cavern, which would be dark if not for the candles we light within it.
Its walls don't behave like proper walls; the East goes on forever towards the undiscovered country of Salt, the South borders on Parabola, the West abuts the Light Beyond Hell, and the North tapers to a point.
Most of all, it was created to be a hiding-place, a refuge, a shelter from the pitiless verdict of the stars. "Rock of ages, cleft for me / let me hide myself in thee."