I love intentionally taking pit traps to find secrets in Dungeon Master, sometimes the combination of pit traps and teleports leading to entirely separate branches of the dungeon that need to be explored.
I also love encountering peaceful areas in a dungeon, especially if they come as a surprise. Ultima Underworld won me over when I reached the home bases of the two orc tribes and realized I could interact peacefully with them. This might have been the biggest influence on how I design dungeons myself