From the harbour, Pósthússtræti leads south past the bars and restaurants of Tryggvagata, Hafnarstræti and Austurstræti to Vonarstræti and Tjörnin, invariably translated into English as “the lake” or “the pond”. Tjörn and its genitive form of tjarnar are actually old Viking words, still used in northern English dialects as “tarn” to denote a mountain lake. Originally formed by a lagoon inside the reef that once occupied the spot where Hafnarstræti now runs, this sizeable body of water, roughly a couple of square kilometres in size, is populated by forty to fifty varieties of birds – including the notorious arctic tern, known for its dive-bombing attacks on passers-by, and found at the lake’s quieter southern end. The precise numbers of the lake’s bird population are charted on noticeboards stationed at several points along the bank.