ARP Portal K??? (K1A tunnel - mid) [????- ]
This is the middle portal for tunnel K1A.
The marker's position is approximate - it's definitely along the lane behind the buildings, but I'm not sure exactly how far along. It's obvious to see when you get there, just look out for this door in the cliff:
I took a photo through that small hole in the door next to the vent. It's too dark to see much, but it's clearly a tunnel: