You Encounter a Door

Wer looks up at the conceited Sorcerer and waves him away.
Transforming into a Bat, Wer flaps after the supercilious Human.
Out of defiance, Wer decides to remain in that form for the next few hours.
Once on the other side, there's a great deal of equipment strewn about the sand.
It is all of Meldo’s load, but there are several things here that could be useful. (Including some food and oil.)
Meldo seems quite pleased at the company, but then again, it could just be the light.
After a cursory examination, Kruddo realises why the Mule was left behind; the cavern exit this side is too small for any large creature to pass through.
Leaving Meldo behind, the adventures press on.
The narrow passageway slopes steeply down at this point but then widens and flattens out about an hour later.
There are several smaller tunnels leading off the main one, but Wer has no desire to explore them on her own.
The small group continues down the wider passageway.
They travel on for another two days.
(Any rations? Ask Sven!)
Despite posting guards at night you encounter nothing but a few strange looking/sounding bugs.
The next day the tunnel starts to open out and signs of stone working can be seen.
A few hours later you come to a proper passageway. The walls and floor are not remotely perpendicular though. Kruddo is actually offended by it. Although the masonry work shows some skill, it lacks patience and planning.
The long corridor ends with a large but plain stone door.
It has a small ‘hatch’ in the upper part and a large metal knocker around three feet from the floor.
There are no visible hinges or lock mechanism on this side of it.
The hatch is about seven feet above the floor and firmly shut.

What do you do?

1) Any equipment taken from Meldo will add to individual encumbrance!

2) Two more rations (If you have them) are gone per person including the dog but not the snake.

3) If you do not have any rations left, you start to starve!