Both of them froze in shock.
Gu Zheng aimed his flashlight at the opening.
Inside, a neat flight of steps did indeed lead underground.
The hatch was an iron plate almost the same color as the concrete.
It was exactly like the one they had seen in that factory building in Yanling.
They exchanged a look, then decided to go down and investigate.
"Wait!"
Before they descended, Song Ning took Gu Zheng's flashlight and searched the floor around them.
Then she pointed at a cast-iron component roughly a meter square.
"Move this to the opening first. If this is like the tunnel last time, the iron plate will close once we go down."
Gu Zheng bent down and moved the lump of iron onto the steps at the tunnel entrance.
That way, even if the plate closed, it would get stuck.
Only then did they enter the tunnel and head forward.
In theory, they should have been safe.
A layer of dust covered the factory building above, proving that no one had been there for a long time.
And the main breaker had initially been switched off.
That suggested there should be no one in the passage, because without power, the entrance could not be opened at all.
Sure enough, the passage was dusty too, with a noticeably thicker layer than upstairs.
Their footsteps stirred up faint clouds of dust that even made them cough a little.
If no one had visited the factory building above for nearly a month, this underground area must have been deserted even longer.
They followed the passage forward.
Sure enough, after some distance, they reached another flight of descending steps.
At the bottom, a row of rooms appeared on their left.
The layout was still exactly like what they had seen underground in Yanling.