Advanced Adventures #1: The Pod-Caverns of the Sinister Shroom is a short adventure designed for 6 to 8 characters of levels 2 to 4. Written using OSRIC (the Old School Reference and Index Compilation), it is largely compatible with Advanced Dungeons & Dragons 1st edition. From the publisher's website:

Strange doings are underfoot in the wild hills bordering the realm of decent and civilized folks! Villagers and cattle have gone missing; woodcutters have disappeared; misshapen beings have been seen shuffling through the forests. Some brave villagers have tracked a group of stolen oxen as far as the rocky banks of a small river in the hills. The trail disappeared down into a fissure in the limestone rock, where a fast-running stream plunges down to the dark caverns below.