How can I get the starstone after I drop it?

Hint 1 of 5:

It has strange spatial properties.

Hint 2 of 5:

It's sort of in two places at once. One location (the one not where you drop
it) is where it's real.

Hint 3 of 5:

So when you drop it in the building, it's not really there. Note that you
don't get points when you drop it there.

Hint 4 of 5:

You need to drop it somewhere else outside.

Hint 5 of 5:

Remember the wooden notice? The last word was 'starstone'.