Länsi-Musta, Suomenlinna
You'll get in here via the smaller island, which is a military
area. It means that in the island of Pikku-Musta you're not allowed
to turn off from the road. That's all, no special permissions
required to walk through.
Should you need to know, the ferries to Suomenlinna depart from
the Kauppatori market square (cf. the user's web page for
coordinates). The cache shouldn't be too hard to find.
