As per this post:
CHALLENGE OF THE FROG IDOL
Written for Labyrinth Lord
For characters of Level 3-6
by Dyson Logos
Get it here.
CotFI is a site-based wilderness adventure with a sort of dark 'lost empire' feel, set in the Black Mire and the nearby city of Coruvon. The PCs travel around the swamp looking for the missing treasures of the Frog God, a stone statue which speaks but retains little of its former power. In exchange, it'll give them a magic item which will help them enter the dwarven fortress of Kuln, now taken over by giants. Overall, it's the kind of thing people have seen before: a swamp adventure with lizardmen, troglodytes, giant carp, etc. and some twists and turns.
I don't know if it could be called a "true hexcrawl", but the Black Mire is big enough for the PCs to explore, get lost, travel for days, run out of food, get distracted by side areas and get worn down by random encounters. The treasures can be gathered in any order and a few of the encounters allow for varied strategies, although many are straight up slugfests.
Several locations on the map (including the ruined fortress of Kuln) are left up to the GM's imagination, so you can use this adventure as a jumping-off point for adventures in your own dungeon or more exploration into the Black Mire.
I would absolutely run this module myself. It would probably take my group 6+ sessions to get through it but they are notorious newbies and more seasoned players could doubtless do it in less time. My favorite bits: an island made out of zombies which floats around the swamp, and monstrous tentacles reaching out from under the wooden causeways to drag PCs into the water.
And just sayin', but you should probably play this song at some point in the adventure.