Which episode?
Had some floor that opened up and had a pit of hot rocks below and the door would lock and the floor would open with the victim falling into the pit of hot rocks/coals ten feet below to their deaths?
I saw this as a little kid and haven't seen this show in over 40 years but this episode stands out to me.
It seemed like there was some type of door handle the victim grabbed onto to hang on but then even that retracted into the wall and the guy falls in. Bill Bixby is caught in this trap later in the episode but somehow he survives, it has been too long and can't recall how he escapes.