When one goes to one's favourite tavern, it is preferable to be able to quaff one's ale in peace...
Here is a generic, system neutral 'dungeon-crawl' style adventure involving clearing a fairly complex inn cellar of all the unwanted visitors. The landlord (or someone) keeps quite a lot more than barrels of ale down there, but it's been overrun and someone - read the characters - gets hired to sort things out.
There is extensive discourse about how to fit the various creatures (and traps) into whatever game system you are using. It will possibly work best with early versions of Dungeons & Dragons or one of the 'Old School' fantasy systems, but ought to work with any fantasy system that you have to hand. Naturally, you will need to put in some prep work to have the appropriate game mechanics for monsters etc. before you begin (or be confident in either remembering them or looking them up quickly in whatever bestiaries you have for your chosen system).
The actual 'dungeon' comes as 2 pages - a nice clear coloured map and a key with single-line notes on each location down there. You won't need more, the map shows what is in each location well enough for you to explain it to your players.
One nice touch is that the explanatory notes on traps actually has a diagram of how they work. Nice for the mechanically-minded, and easy for you to describe and to check if someone saying he's checking for traps has looked in the right place, or disabling it has actually done so. Naturally, most of us do this by die-roll, but you can make some vivid descriptions.
A neat little package that should supply an evening's entertainment for you and your group, with fairly minimal but necessary preparation.