Lake Thun is the larger and more castle-studded of the two lakes that flank Interlaken, running 18 kilometres west towards the city of Thun. Its northern shore carries a railway and a road, but the southern bank is quieter, with the Niesen — a near-perfect pyramidal peak — rising above the village of Spiez on a peninsula jutting into the lake. Oberhofen Castle, with its turrets reflected in the water, is one of the most photographed castles in Switzerland.
The BLS lake boats run a regular service from Interlaken West, stopping at Gunten, Oberhofen, Hilterfingen, and Thun. The full crossing to Thun takes about an hour and forty minutes each way. A day cruise stopping at Spiez and Oberhofen Castle makes an excellent half-day excursion — the boat journey is the point, not just the transport.