Port Used: GZDoom 4.11.3
Skill: Ultra Violence
There is, in fact, no way of knowing that the yellow key secret is there, barring pressing on every wall in every room and eventually getting lucky. Ugh.
Also, I was mistaken when I mentioned that Maniac Mansion was a Sierra game. It was also created by LucasArts (or Lucasfilm Games, as it was called at the time).
Chapters:
00:00:00 E4M5: The Salt Mines
00:27:55 E4M6: Alcatraz
00:37:22 E4M7: Devil Canyon
00:55:21 E4M8: The Crawling Chaos
00:58:46 Intermission Text
00:59:47 Outro