For land environments, I can’t think of any that have been unused, but for aquatic adventures there are a few possibilities:
- Coral Reefs - a whole maze full of creatures
- Sargasso Sea - Vast mats of impassible plants containing wrecks, hidden islands, etc.
- Deep-sea vents - the closest thing we have to an alien environment on earth…
The Plain of Jars. Thousands of giant stone jars on a plateau in Laos. Many contain bodies. No one is entirely sure who built them or why.