We are here in Bohonal de Ibor in the Extremadura, a hot and dry area in southwestern Spain. However, this is also the river basin of the Tagus River (Tajo) which rises in the northeast of Spain (between Teruel and Cuenca) at an altitude of 1590 m. It has a length of more than 1000 km and is thus the longest river of the peninsula. The Tagus flows westwards and forms, over a distance of 60 km, the border between Spain and Portugal, before flowing into Portugal as the river Tejo. At the Portuguese city of Santarém, the Tagus can be sailed. From here on the tidal effect from the Atlantic Ocean is already perceptible. Finally, before Lisbon, the river flows into an estuary, which is an important natural port but also a valuable nature reserve.