Steps indoors (9)
I believe the answer is:
staircase
'steps' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for staircase that I've seen before include "Route between floors" , "Way between floors" , "Set of steps" , "part of the mansion?" , "It's Caesar (anag.)" .)