This scenario was Dyson Logos' answer to the Fat Frog Challenge presented by JB on his BX Blackrazor blog.
From the Introduction:
The Frog Idol has stood in the Black Mire for ages untold - an idol of an ancient and forgotten god who now only manifests through this ancient rock in a forgotten place. However, with the conquest of the dwarven citadel of Kuln by the giants, adventurers have been seen again in the city of Coruvon. And from Coruvon, the Black Mire is always in sight.
This adventure is designed as a site-based adventure setting for a party of characters of levels 3-6 set in the Black Mire west of the city of Coruvon.