A lot of people have complained that its not a fun chapter because its too confusing. To make it unconfusing, I have made a map (not to scale), showing that On A Rail isn’t really very complicated, it just folds back on itself a lot. Isn’t it neat?
0.1 entrance from Power Up; barney; gate; switch for gate at 0.1
0.2 elevator down; exit to 1.1
1.1 elevator up; entrance from 0.2
1.2 flooded track; electrical hazard
1.3 ramp up
1.4 ramp up
1.5 revolver ammunition
1.6 electrical hazard
1.7 crane hook blocks progress; houndeyes; bullsquid
1.8 houndeyes; entrance to corridor
1.8.A bullsquid; dead HECU
1.8.B HECU; headcrab ambush; rocket thrusters
1.8.C houndeyes; switch to extend bridge at E
1.8.D flooded room; bullsquid; extendable bridge
1.8.E bullsquid; dead HECU; grenades; satchel; broken elevator
1.9 bridge; bullsquid; barnacles
1.10 bullsquid; buckshot; stairs
1.10.A catwalk overlooking 1.7; revolver ammunition
1.10.B automatic turret; switch to remove crane hook at 1.7
1.11 elevator up; HECU; exit to 2.1
2.1 elevator down; entrance from 1.11; revolver ammunition; smg grenades
2.2 alien slaves; switch for 2.5
2.2.A stairs up; alien slaves; headcrabs
2.2.B HEV suit charger
2.3 HECU
2.4 HECU; player controllable turret; switch for 2.6
2.4.A stairs up
2.4.B HECU
2.4.C HECU
2.4.D alien slaves
2.4.E revolver ammunition
2.4.F stairs down
2.4.G HECU, alien slaves, revolver ammunition
2.5 gate
2.6 gate
2.7 tripmines
2.8 HECU
2.8.A HECU; alien slaves
2.8.B barney; revolver ammunition
2.8.C HECU; headcrabs
2.8.D HECU controlled turret
2.8.E tripmines
2.8.F tripmine; door to 2.9
2.9 rocket ship midsection; ladder down; exit to 3.1
3.1 rocket ship midsection; ladder up; entrance from 2.9
3.2 ladder down from 3.1; revolver ammunition; trip wires
3.3 automatic turrets; bullsquids
3.4 dead HECU; bullsquid
3.5 HECU controlled rocket turret; tripmine
3.6 tripmine
3.7 gate
3.7.A alien slaves
3.7.B alien slaves
3.7.C stairs up; tripmine ammunition; satchel
3.7.D HECU; switch for 3.10
3.8 tripmines
3.9 train
3.10 gate
3.11 player controllable turret; HECU controlled turret; HECU; switch for 3.12
3.12 gate
3.13 satchels; ladder up to HECU at 3.14; SMG grenades
3.14 elevator up; exit to 4.1; HECU
4.1 elevator down; entrance from 3.14
4.2 electrical hazard
4.3 tripmines
4.4 moving boxes overhead; HECU ambush; gate; switch for 4.4
4.5 ramp up
4.6 moving boxes overhead; tripwire; automatic turrets
4.7 HECU controlled rocket turret
4.8 electrical hazard
4.9 ladder down to 5.1