From Tekkenpedia

Hell's Gate
Walls	Yes
BG Music	Ka-En-No-Mai

It's possible that this is yoshimitsu's stage

Hell's Gate is a stage in Tekken 5. It is a dark and demented stage, in which a red sky lingers overhead, illuminating all with a sinister crimson glow. Also, there is a full moon in the red sky. There is a gate in the area, which looks like it leads into a vast sea of red. A jungle beat is playing in the background, and there is a heavy emphasis on the drums. There is also a concrete human head with a concrete hand on either side of the concrete head in front of the player.

[edit] Trivia

• Bryan Fury have a sub-boss fight here.