Kotka's defining attraction is Langinkoski Imperial Fishing Lodge, a Tsarist-era log cabin built for Alexander III on the rapids of the Kymijoki river — a genuinely evocative place to spend an afternoon. In town, the Maritime Centre Vellamo is the most architecturally striking building on the waterfront, housing three museums under its wave-shaped roof, and Maretarium presents Finnish freshwater fish in naturalistic tanks along the Sapokka bay.
Kotka's waterfront and archipelago are the other main draws: the harbour area makes for good walking, and boat trips out into the island-scattered coastline run in summer. The Kotka-Hamina coastline is one of the wilder parts of the Gulf of Finland archipelago and worth exploring by kayak or on the ferries that run to the outer islands.