I used to dm AD&D way back in the day (1980's, yes I am old). I was quite a terror when I wanted and these were two of my favorite rooms in this one dungeon of evil I devised:
1) Party enters room and the door promptly shuts, no handle or anything on the inside. Contents of room fairly basic, mostly a few "stone" tables and some (completely useless once examined) scrolls. Walls of room as well as the inside of the door all appear to be made of some weird, unknown material, covered in strange symbols (once again, completely useless). Knock spells do not work, and there is nothing that would allow the use of lock-picking. Any attempt to break down the door (damaging) will cause holes to appear, from which a strange, red viscous fluid would start flowing out. Unchecked the fluid would completely fill the room within 2 "turns" (20 minutes game time), minus the damage caused to the door, so more damage = faster room filled. Only way out was to damage door, then heal it completely. (P.S. Party almost died before figuring this out, lol).
2) Last room was simply furnished with a single table, upon which lay a beautifully designed sword. By this time, the party decided they didn't want to take any more chances and high-tailed it out of there. After we were though, I showed them my notes, revealing that the room was in fact, completely safe, and that the sword was essentially the equivalent of a +5 intelligent holy sword with the additional property that allowed it to be completely (and safely) usable by ANY class. I was cussed out pretty badly there.