I used this in my 2E game many years ago. The dungeon itself was extensive, and was revisited many times by the PCs... what really set the tone for the place though was the entrance trap.
While not entirely life threatening (to a first level mage it could be deadly), it was actually humorous, and had the unique aspect of working in real life as a prop. In addition, the way the group reacted to this trap was both amuzing and classic in and of itself... which is why it lives today very fondly in my player's memories. 
The Trap (The lure)
At the bottom landing of a set of rough hewn steps leading down into the 1st level of the dungeon, inscribed on the far wall in common in extremely large letters is the word "WARNING!"
Directly below the large lettered warning sign is a messege of the same type, also written in common, and in extemely tiny lettering below is "This dungeon block subject to sudden movement."
The Prop (The set up)
On a piece of blank graph paper write in large red letters... so that it takes up the entire sheet "portrait syle" is write the word "Warning". Then, in as small writing I could manage I wrote, "This dungeon block subject to sudden movement."
The execution (The fall)
Now, describe the scene as above, and hold up the prop about face level your hands on either side of the paper, but do not give it to anyone. Invaribly, a player will get out their chair to try and read the small writing. When they get close, but hopefully before they read the bottom message whack em with it! If you miss, the character makes its save... if you hit them roll a d6 and apply the damage to the player's character.
Amusing for everyone involved, especially the DM. Interestingly, some players will still try to read the message. Whack 'em again! 
In my group, when new players visited the dungeon for the first time the veterns would point out the sign and tell them it was very important that they read the message... then just stand back and watch the fun.
There were two 1st level characters reduced to 0 hps in this manner, both elven mages. The second time it happened the vetern dwarf quipped, "We lose more elves that way..." Which became a table standard quote anytime an elf died in my campaign from then on.