This is a fun turn of events to enliven a quiet night at the local tavern: the bar tender comes up from the cellar panic-stricken because the place is crawling with ferocious lizards! The characters are enlisted as exterminators and off they go...
There's a comprehensive map of the extensive cellars under the Moon Dragon Inn (or if you don't have than, under whatever tavern you choose!) with a second page giving one-line descriptions of the contents of each chamber. There are notes about selecting suitable creatures from the game system of your choice, some choice traps (which don't seem very relevant but maybe those pesky lizards scuttle off into areas not intended for visitors and conscientious exterminators will follow them...) and treasure listings.
A simple side-trek adventure for a single session's play, intended for reasonably experienced but not overly powerful characters (4th-7th level if it's D&D or similar that you play), nicely put together and capable of being run with minimal prep time if a quick 'crawl' is what you and your players are after!