Iseltwald is a village and municipality on the southern shore of Lake Brienz in the Bernese Oberland region of Switzerland. Politically, the municipality is located in the Interlaken-Oberhasli administrative district of the canton of Bern.

Lake Brienz is a lake just north of the Alps, in the canton of Bern in Switzerland. It has a length of about 14 kilometres (8.7 mi), a width of 2.8 kilometres (1.7 mi) and a maximum depth of 260 metres (850 ft). Its area is 29.8 square kilometres (11.5 sq mi); the surface is 564 metres (1,850 ft) above the sea-level. It is fed, among others, by the upper reaches of the Aare at its eastern end, the Giessbach at its southern shore from steep, forested and rocky hills of the high Faulhorn and Schwarzhoren more than 2,000 metres (6,600 ft) above the lake, as well as by both headwaters of the Lütschine, the Schwarze Lütschine flowing from Grindelwald, and the Weisse Lütschine from the Lauterbrunnen Valley, at its southwestern corner. Not far north from Lütschine's inflow, the lake drains into a further stretch of the Aare at its western end. The culminating point of the lake's drainage basin is the Finsteraarhorn at 4,274 metres above sea level.