Aw, sweet! Secret base finding time!
Like Jarre said in the signpost, you're looking for a well-hidden secret entrance; something that's not easily accessible.
If you were a smuggler trying to hide your ill-gotten gains, you probably wouldn't want to transport it too far.
For that reason, it's likely to be somewhere on the docks.
Jarre theorised that the smugglers hide things in a warehouse or similar building - that's not the case.
You're looking for a part of the dock that would be difficult to access on foot.
On the far left side of the docks, there's a support beam that doesn't support anything.
As if that wasn't weird on its own, there are inexplicable hooks embedded in the nearby walls.
This has the makings of a secret area; we just need something that will carry us across the gap.
Preferably, it would embed itself in the overhead beam.
A grappling hook!
They'd probably be very sought-after in a seedy place like this, so you'll have to look for anything well-secured.
There's a boat with a tightly-knotted tarp covering it near the bathhouse.
We've had to deal with knots before; you can make short work of this one.
Use your knife on the tarp.
?
The grappling hook will easily get us across the gap.
Nice, we found the smugglers' storage!
Jarre wanted their kraken-newt carving - it must be around here somewhere.