Faxanadu

The story of an unnamed traveler who returns to his home town, which is part of a massive inhabited tree, only to find it ruined and abandoned because the tree's water source has stopped and is tasked with finding out the cause and saving the tree. The game uses typical sidecrolling and platforming gameplay. However, the game also employs various elements that classify it as a role-playing video game including its expansive story and medieval setting. (Wikipedia)