The answer is:
Look down on the top layer. One long word is very prominently visible. That word is:
When we do that, we can spot another word in the new grid:
Doing that, another new word becomes apparent:
Excavate this area down to level 4, and we get the following new grid, concealing the words:
Excavate this down to level 5 to find:
Excavating this ...
You have lost a:
First note that each clue:
Now we can also see that:
Now use the diagrams. What we have here are:
These can be constructed like so:
So now putting the words in green together, we know you have lost:
The first thing we need to do here is rearrange the 30 tiles in a meaningful way. We can do this by noticing:
What do we have here? Look next at the numbers in the first four columns. These look a lot like:
What might our desired 2-word 10-letter answer be? Well, what do all these people have in common?
The first thing to do is work out what shape each diagram represents. Across each row, these are in turn:
What do we now have? The highlighted cells on these 8x8 grids of squares:
Now, we have identified 16 letters of interest - the same number as the number of "+/-" commands in Step 2 of the puzzle instructions. What we must do next, ...
While @hexomino has made fantastic progress thus far, one thing currently not yet discovered in that answer is the significance of the named buildings. This can be seen by:
EDIT WITH HINDSIGHT: Everything below this line was incorrect speculation, shut down by the OP in comments (by confirming that @hexomino had correctly found 'N' as well) and then made ...