The closest is Forte de Santo António, 1 km north-west of the city centre; the most famous is Ducal Palace of Vila Viçosa — #2,031 of 9,079 worldwide — 48 km north-east. The oldest dated site in the circle is Castelo de Palmela, founded c. 800.
The 100 km circle reaches into 2 countries — Portugal (49), Spain (3).