Answer:
In marble halls as white as milk, lined with a skin as soft as silk. Within a fountain crystal-clear. A golden apple doth appear. No doors there are to this stronghold, yet thieves break in and steal the gold.
I can be short and sometimes hot. When displayed, I rarely impress.
What types of words are these: madam, civic, eye, level?
What is that which, though black itself, enlightens the world without burning?
I am the greatest teacher out of them all, but alas in the end I kill my pupils.
If itβs information you seek, come and see me. If itβs pairs of letters you need, I have consecutively three. What am I?