I am in front of the gate and defeated all the enemies. But how do you open the gate?

I can't click on it nor do I see a lever or anything to open the gate.

The gate also does not open on its own. Is this a bug or do I have to find something or go somewhere?

Close this. I found the tunnel to the left of it. Took me a while

i lol'd, how long did that take you? took me like tops 30 seconds to find the tunnel