Not long after you left for the tunnels, I had Tara do a little digging into our records.
She managed to find some old documents mentioning a Mysterious Instrument located not far from the passageway you found. From what I could gather, its purpose was to activate the properties of Shrinking Potion. One could conclude that it was placed in such a location so that, in the event of a mine collapse, it could be used to help people to safety. Much like the tunnels, however, it probably hasn't been used in quite some time.
The documents also mention Shrinking Goblin Blood and Goblin Saliva as the primary ingredients for the Shrinking Potion needed to operate the device. I believe these items can be obtained from a Cruel Goblin Butcher and a Goblin Scourge.
Collect these and bring them to me as quickly as you can!
What the documents failed to reveal was who invented this Mysterious Instrument, Jessie mutters, looking somewhat disappointed.
I can't locate a name anywhere!
Still, I somehow feel a closeness to the inventor of this fascinating device. I wonder who it could be?