This appears to be the Entrance to the Mine Port, Player.

But Stua told me we need a key to open the door.

The person who has the key to the Secret Port Entrance is probably higher-ranking.

Take out the Mine Supervisor and the Mine Overseer. I'll take care of the others.
You're back already? I knew the overseer had it!

Are you sure it's the Key to the Secret Port?
I think we've come to the right place. Let's take the secret entrance to the Mine Port, quickly.

Are you ready?
(This is the Secret Port Entrance.)

(It leads to the Mine Port.)
We should think through our next steps carefully.

Give me a little time.