Have a door which opens through the "large castle gate mechanic"(spin a lever pulling a chain - which in turn pulls the door upwards). In this case though, the lever is broken - so the player has to stack barrels/boxes in a temporary-solution-scrawny-built "cage" which counterweights the gate and pulls it upwards.
Or.. pull out bricks from the wall, which become stepping-stones revealing a jumping path leading to the next room through a cracked wall/window higher up on the wall.
Or.. Have the wall opposite to the door be under construction (stupid illustration);
Have the player somehow break loose the "fat wooden board", which swings across the room and smashes the door open.