Forming a natural border between Switzerland and Germany, the long Bodensee – often anglicized to Lake Constance – is a huge bulge in the course of the Rhine, some 67km from end to end. Unlike most of the Swiss lakes, it doesn’t have the benefit of shoreline mountains, and so is exposed to winds year-round and experiences particularly rough weather in the winter. During spring 1999, when the combination of heavy rain and an unusually large quantity of snowmelt in the Alps led to major flooding throughout the country, the lake rose to its highest level for more than a century – many coastal towns were flooded, and even as late as August the harbour fronts at Rorschach and Stein-am-Rhein remained underwater.

Three countries border the lake. The head of the lake, at the extreme southeastern corner, is Austrian, focused around the genteel town of Bregenz. The northern and northeastern shore are lined with German towns, largest of which is the cosmopolitan city of Konstanz, separated from its contiguous Swiss suburb of Kreuzlingen only by an arbitrary international frontier. Haze and lingering fog can often mask the views across the water, but this hasn’t stopped the lakeshore becoming one of Germany’s main summer-holiday destinations; this rubs off on the southwestern, Swiss shore, too, where the scattering of soporific little resorts such as Rorschach and Arbon have a strong Teutonic air about them.

All three countries have their own boat operators on the lake. The main Swiss one, covering journeys between Rorschach and Kreuzlingen, is the Schweizerische Bodensee-Schifffahrtsgesellschaft, based at Romanshorn harbour (071/463 34 35, www.sbsag.ch). Journeys west up the River Rhine from Kreuzlingen to Stein-am-Rhein and Schaffhausen are operated by the Schweizerische Schifffahrtsgesellschaft Untersee und Rhein, based at Freier Platz 7 in Schaffhausen (052/625 42 82, www.urh.ch).

There are dozens of excursion cruises all round the lake during the summer season (April–Oct), in addition to the regular summer ferry routings which, on the Swiss side, hop their way from Rorschach to Kreuzlingen. In the peak season (June to mid-Sept), it’s possible to spend a day on the lake, leaving Rorschach at 10.55am for the two-hour cruise to Kreuzlingen, where you have an hour or so for lunch before departing at 2.05pm on the gorgeous journey on the Untersee and down the Rhine to Schaffhausen, arriving at 5.25pm; the other way, going against the current, takes from 10.30am to 6.25pm. Some boats cross from the Swiss shore to the German side, stopping at Friedrichshafen, Langenargen or Lindau, as well as Bregenz in Austria. From Kreuzlingen, boats also shuttle over to Konstanz, and to other German destinations such as Meersburg, Überlingen and Radolfzell. Year-round car ferries run between Romanshorn and Friedrichshafen, and between Konstanz and Meersburg.

While InterRailers pay half-price on journeys along the Swiss shore, Eurail and Swiss Pass holders travel free. The Thurgau Day Pass covers free journeys along the Swiss shore and from Romanshorn to Friedrichshafen. The Bodensee Pass (Fr.40 for 15 days) gives half-price travel on boats, trains and buses all around the lake; holders can buy Bodensee Day Passes (Fr.28 per set of three), valid for free boat travel on the whole lake and the Rhine as far as Schaffhausen.