Looking for a low level adventure with fantasy elements while having a possible post apocalyptic or gonzo D&D setting? Well 'The Red Demon In The Vile Fen' combines all of this while having the advantage of being completely free.
Grab It Right Over
The Dungeon of Signs blog put out a fantastic old school adventure called 'The Red Demon In The Vile Fen' an adventure for LL for PC's levels 2-4 with a very distinctively gonzo old school campaign feel. The adventure takes place in a swamp land infected with hoards of froghemoths, a weird science fantasy atmosphere and lots of opportunities for PC death and dismemberment.

According to the author there are a ton of adventure hooks and swamp encounters with the high weird and the incredibly strange just waiting around the next tree :
So called because of the bright red corrosion marking its huge hull, the Red Demon is an ancient war machine decayed and destroyed, but still menacing. A large tank like vehicle standing 100' tall and over 100' long, the Demon mounts a massive cannon hanging obscenely from a turret shaped like a grotesque head and rests partially submerged in the noxious swamp. The Vile Fen is full of such sites, and the Demon is only a small machine, compared to some of the ancient monoliths deeper within its murky embrace
The nearest fishing village knows of it but stays far clear, traditionally because the radioactive sludge leaking from it made it deadly to approach. The flora and fauna have returned near the wreck in recent years and flourish, but in his youth the headman's local brother attempted to explore the Red Demon and never came back, cementing the artifact's evil reputation.
Let me see where do I start with this adventure, there is so much awesome. From the sci fi elements to the weirdness of the adventure itself. The artwork is pretty awesome and there's lots of solid adventure encounters worked into the background. This adventure could easily be reworked into a classic post apocalyptic campaign with little modification . And even a possible Lamentation of the Flame Princess low level campaign jump off point. The author does a nice job of setting the stage and the artwork adds to the gonzo flavor of the piece in a solid way that makes me want to run the whole twelve pages for a group of players who will not be expecting the whole effort. There is also a possible adventure jump off point for other OSR products and adventures here as well. I'm thinking of Carcosa or some other Saturday morning or Lovecraft style product here. All in all this is a great find to add to the OSR DM's tool box!