I am not talking about the MRT system. I see that everyday.
I am currently in Singapore and I swear I haven’t seen daylight in two days. My hotel is directly connected to this MRT and Mall. I am just underground and everything is so huge down here.
I wonder is this a city under the city?
I know we have maps like that for the (publicly accessible) tunnels under Chicago, I’m sure someone has done the same for your city.