Pick a door, clear the room behind it, take what it pays. Three rooms, the Courtyard, then the Mirror. You start with 10 rounds, and every headshot kill hands the round back. Health only refills within the segment you're in. Die and the run is over.
The classic route is the original linear map, with unlimited spare rounds.
Controls
WASD Move
Shift Sprint
C Tap crouch, hold prone, slide while sprinting
Z Prone
Space Jump, stand up, cancel a slide
RMB Aim down sights
Shift Hold breath while scoped
LMB Fire
R Reload
T Swap optic
Esc Pause
Settings
Best runs
Click to lock the mouse. Best played with headphones.