when you press the Alt key you can see the door. to get through it follow these steps.
It seems after you meet Dr.Elrath and tell him about the canister,
he says that his cellars key was stolen by someone. The only way to find out
is to find his door key behind his house (use ALT)
Here is how to get through his house
First click on the lantern to the
right of the entrance to open the bedroom door, then the one on the west wall
to open the southern door. Go through the southern door into a small room
with another locked door to the south. Click on the lantern in this room to
close the door you just came through and open the door to the south and the
door to the bedroom. Go on through the open door and go into Elrath’s bedroom
and click another lantern on the north wall near his bed, this will open both
doors leading back to the first room. Now go back to the first room and click
on the west wall lantern again, this will close the two southern doors again.
Click on the west wall lantern a second time to open the southern door. Go
into the small room and click on the lantern to open the south door, and the
door to the basement should be open.
