Triboldingerbohl, also known as Triboltingen or großes Bohl or Langenrain, is the fourth largest island of Lake Constance, with an area of . It is long and up to wide. It is located in the easternmost part of the Untersee (Lake Constance), near the point where the Seerhein flows into the lake. This part of the lake is also known as the Rheinsee. It belongs to the Wollmatinger Ried nature conservation area; administratively it belongs to the district industrial area of the City of Constance. Until 1934, it belonged to the municipality of Wollmatingen, which was then annexed by Constance. Triboldingerbohl lies southeast of Reichenau Island and from the dam that connects Reichenau to the mainland. The area between Triboldingerbohl island and the Reichenau dam is called Ermatinger pool and is an ecologically important shallow-water zone.
Triboldingerbohl is uninhabited. It is a bird sanctuary. It takes its name from the former Swiss municipality Triboltingen, which was located on the souther shore of Lake Untersee. Between Triboldingerbohl and the mainland lies the smaller island of Mittler Bohl, also known as Langbohl. The two islands are separated by a channel which is only wide. This channel and the channel separating Langbohl from the mainland are collectively known as ("tubes").
Both island are covered with reeds. They consist of a several meters thick layer of Schnegglisand, a calcareous deposits from Blue-green algae), which is covered by a layer of humus.
Although the island is uninhabited, it is listed in the Constance street directory. It falls under postal code 78467 (Constance-Wollmatingen).