The castle is located on the eastern Lake Zurich's western Obersee lakeshore in Rapperswil, a locality of the Rapperswil-Jona municipality in Switzerland's canton of St. Gallen.

Rapperswil Castle dates back around 1200 to 1220 AD, and it was first mentioned in 1229 on occasion of the foundation of the Rüti Abbey.

The castle and the fortifications of the former locus Endingen (given by the Einsiedeln Abbey) were built by Count Rudolf II and his son Rudolf III von Rapperswil, when the nobility of Rapperswil moved from Altendorf (Alt-Rapperswil) across the lake to the other side of the so-called Seedamm, maybe to establish their own parish church and to avoid to go the mess, by crossing the lake, in St. Martin Busskirch.

In 1350 an attempted coup by the aristocratic opposition (a central person was Count Johann II) in the city of Zurich was forcefully put down, and the town walls of Rapperswil and the castle were destroyed by Rudolf Brun.

The highest tower in the southwest is the donjon, commonly called Gügeliturm in Swiss-German language, where the so-called Hochwächter warned the residents against approaching danger or fire.

[9] After hours visits are available by appointment, as well as guided tours for groups, although the castle is just partially accessible for the public.

The impressing Rittersaal (knight's hall) and the historical wooden architecture, as well some pictures and tapestry include further points of interest.

The city and local board of Rapperswil-Jona initiated in 2011 a new service and operating concept for the Rapperswil castle to provide the site as a touristic attraction and meeting place, and thus recognizable as a brand.

It is also assumed a predecessor building, a Roman era watchtower in conjunction with the Vicus Centum Prata, but for the present there are no archaeological findings.

Likewise, there are few reliable data for the construction, only the renovations and the function of the castle are therefore secured by historical sources.