the cottage key

You discover a note
that leads to a cottage
with a welcome mat. Under
the mat it says there's a key

that fits any lock

and can make any door
open onto any other door
in the world. Using the key,
you just slide it in. Visualize
the destination door, turn the key

and open - and walk

on through.

But you have to leave the key behind.
"The key is yours," the note says.
The note gives you all
the rules.

So you have the note.
Do you go to the cottage
and lift the mat, take the key
and if so? Where do you

open the door through to?
How will you explain
where you've gone
when you go?