The secret area by a barnacle outside the Blast Pit center. :>
Answers to the unguessed HL2 ones from me:
3: d1_town_03 (I think, at least it’s the skippable one)
5: canals_13 (Inside the big red silo)
8: Citadel_03 , just after the elevator ride , first puzzle where you have to take an energy orb out of its tube to shut down the forcefield. Looking down.
9: Coast_10 , standing on the lighthouse and looking into the skybox hills.
B: canals_05
Right!
Happy guessing!
No, bro.
GCs is unfair, all the rooms look the same. lol
Btw S, B is d1_canals_07
Nope, it’s 05
That’s obviously what I meant, duh
This is an Apprehension map, where the Ichthyosaur eat the scientist (the one in this picture)
Right? 
Nope. It’s “We’ve Got Hostiles” just outside the first elevator.
Alright, since no one guessed the GMC map (I didnt know it either, but the rules dont say anything about it), I’ve made an easier picture for guessing.
Yes, S. You can have it, its done.
(drawn completely from memory!)
coast_01
Lol, I love how the suit says S instead of L
d2_coast_01
The first map of We’ve Got Hostiles. (Scientist skip to the very left of the picture)
Correct S.
1
2
- The long elevator above green sludgy goo in Blast Pit, right before the tentacle monster. (easy)
- Very first map of HL1 (not including inbounds)