Dionisio Foianini Triangle
Triángulo Dionisio Foianini (Dionisio Foianini Triangle) is the name given to a small area of land in southeastern Bolivia, between its borders with Brazil and Paraguay. Its importance lies in the fact that part of the border is marked by the Paraguay River and, as a result, Bolivia has a water route to the Atlantic Ocean that does not involve Brazil.
Source: Wikipedia — Dionisio Foianini Triangle (CC BY-SA 4.0)