I think Flamelurker's arena in Demons Souls (original and remake) looks visually impressive.
Other fire areas I like
Lower Norfair (Super Metroid)
Fire Temple (Ocarina of Time)
Brume Tower (Dark Souls 2)
Stage 1 of Dracula X
What about you?

Other fire areas I like
Lower Norfair (Super Metroid)

Fire Temple (Ocarina of Time)

Brume Tower (Dark Souls 2)

Stage 1 of Dracula X

What about you?