Breakdown of В коридоре слышно, как лифт медленно поднимается вверх.
Questions & Answers about В коридоре слышно, как лифт медленно поднимается вверх.
В коридоре means in the hallway/corridor and sets the scene (location) first, which is very common in Russian.
коридоре is prepositional case (also called locative in some contexts) after в meaning in/inside: в + prepositional → в коридоре.
Слышно is a predicative adverb used in an impersonal construction. It literally means something like it is audible / one can hear.
No specific listener is named; the idea is “from the corridor, the sound is audible.”
Because как лифт медленно поднимается вверх is a subordinate clause dependent on the main clause В коридоре слышно. Russian typically uses a comma to separate the main clause from the subordinate one introduced by как.