The Castle of Estremoz crowns the old town with a medieval keep, marble details, and the former royal palace that now operates as a pousada. It began as a frontier stronghold, and the view from the top still explains why this hill mattered: Alentejo plains stretch away in every direction, with Spain not far beyond the eastern horizon.
The surviving tower, arcades, and palace rooms make the castle more than a shell. Even if you do not stay in the pousada, climb to the upper town for the approach through narrow lanes and the contrast between military stonework and polished marble.