You have this level that takes place on a mountain, and the devs wanted to have a spot where you could see the gloomy landscape below with more mountains silhouetted in the distance... except this was the PS2 so it's just two jpegs, one for the sky so you can get some parallax and a curved panoramic one for the landscape. It still looks decent enough 
This era was interesting since you could have pretty detailed character models and environments but still had to use fake backdrops and other tricks for larger environments. Makes you feel like you're on an old movie set
The opening tanker level in MGS2 famously did the same thing. I had the Substance bonus disc where you could view all the 3D models and levels in the game and IIRC you could take the camera under the floor and see the mirrored geometry just hanging around there