Fun fact: the ending of the 343 Guilty Spark level in halo is hundreds of feet lower than the beginning of the level, despite nearly overlapping, because there is a surprise elevator that goes down instead of up halfway through and the level never makes up the altitude.
edit: bonus image: 
I FREAKING KNEW IT. I KNEW THAT LEVEL NEVER MADE SENSE!
You go down, then up half, then down full, then up full. It never made sense.