I always found the atmosphere at Belthasarīs lair in 2300 A.D. to be one of the strongest in the whole game.
The horrible future surroundings combined with that mysterious piano track gives me the shivers every time.
Itīs like a weird dream, and no doubt one of my favourite moments of the game, even though itīs also a bit uncomfortable.
I could listen to the piano melody all day and get the same feeling every time!