Day 3: First dungeon you explored as a player-character or ran as a DM.
When I was started out with D&D, there were a bunch of us and we made each other copies of the various books. We did this because we were all poor high school students and because we were enthusiastic about the game, we wanted to share it with each other. Thus we couldn't run any published dungeons. Therefore all of the dungeons were homemade. I do however, remember a couple of "highlights" from my first dungeon exploration...
As we approached the dungeon entrance, there was a phone booth outside with a spray paint can next to it (our starting games were often littered with anachronisms). There was also kobold guard standing out front. Since it was our first game we had no idea what a kobold was or how tough they were. We were unsure how to proceed. Then the phone started ringing. A kobold guard came out to answer the phone. Having seen this before, one of the players ran up and started spraying the can all over the phone booth. The kobold was so frightened it had a heart attack and died. We then looted the corpse of a few coppers and its weapon.
In one section of the dungeon we came across a pit. Inside the pit was a rust monster, which by then we knew about and disliked. Next to the pit was a bazooka (I did mention we had a lot of anachronisms, didn't I?). I picked up the bazooka and started blasting the rust monster until it was dead (it took several shots as a bazooka didn't do a lot of damage).
We never knew what to expect back in those days. Fun times.