Bypassed A3

Scaled down entire map by roughly a third of its size, and redesigned mid and base entries significantly.

Reworked the vents and various interconnecting areas, reducing a lot of empty/unnecessary space and (hopefully) improving navigability.

Redesigned the drop ceilings from scratch, including preventing engineer buildings on top of the breakable surfaces.

Note: added an A/B test of trigger-based vs brush-based ladders, and I can't decide which one "feels" right. Would love any opinions on it.

Reduced trigger_hurt on train so that only the front of the caboose kills.
Added trigger_hurt to opposing wall so that riding train "through" the map wall does kill.
Added ladders and collision objects to create a path over and across the train station shelter.