And old point and click dos game. Graphics quality is less than Kyrandia, but not as homely as monkeyisland.
Things I remember 100%. There is an old airplane in a dark field that requires a "crank" to start. Once you start the airplane there's a short flying scene. There's one point where you are in a swamp/bog, and there is a "frog monster" that you talk to and interact with.
Speculation. the frog monster can give you a gem. You might be collecting treasures. There might be a group of men trying to catch you as you travel around. i think around the scene with the airplane, there's a ruined fort. Don't remember much else other than a lot of the game has this "dark" feel to it.