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: 
The elevators are the big vertical shafts. You start on the left area and take the leftmost elevator (the shaft connected to the gray exterior model, labeled A) down, then walk around that area until you get to the second shaft B. That shaft is the surprise one and brings you down to the lowest level. The third shaft, C, falls apart when you try to use it, and you escape via the fourth one, D, that connects to another gray exterior model and the second (lower) exterior section.
thank you for taking the time to explain!