The First 15 Minutes of Hydra Castle Labyrinth (Dreamcast)

Copied from MobyGames:Heavily inspired by Konami's Maze of Galious, Hydra Castle Labyrinth tasks you with reclaiming a stolen crown from the Hydra that awaits you inside its castle. The game is divided between an overworld and eight different dungeons that can be accessed once you have the corresponding keys. There is no map to tell you where to go and many of the game’s secrets are hidden inside walls or are only revealed when every enemy in a room is slain, requiring players to explore and experiment to gain an advantage when challenging the dungeons.

http://www.nicovideo.jp/watch/sm41527006