Pike's Gut — Hauensuoli in Finnish, "Pike's intestine" for its narrow winding shape — is a granite cleft between two small islands a few kilometres off Hanko's southern shore. For centuries it was a natural harbour where ships could anchor in any wind direction; the polished granite walls are covered in inscriptions left by waiting sailors, including the coats of arms of Hanseatic League merchants and Swedish naval officers.
Visiting requires a boat. Several Hanko operators run summer tours; a typical trip combines Pike's Gut with the lighthouse on Russarö and lasts about three hours. The cleft itself is short — perhaps 100 metres — but the density of carvings is genuinely remarkable. Bring a torch to see the inscriptions deeper in the shadows.