So the bold stuff just interrupts my thoughts. Full sentences are there but they are written unnatural ways that just interfere with understanding. Too many parenthetical asides. There is no need for the bold headers.
Reformatted as something like:
An arched passaged worked into the stone descends down a 20' staircase into deepening gloom. The stairs are caked with centuries of dust. There is a dank mildew smell rising from below.
Footsteps on the stairs echo unnaturally, and magically attuned characters (DC 10 Arcane check) feel a sense of menace at each sound that disturbs the silence.
If the dust is brushed away and the stairs examined, a DC 10 Appraisal check determines that at one time an object heavy enough to scratch the stone was dragged up the stairs.