The closest is Palace of the Dukes of Braganza, 1 km north of the city centre; the most famous is Castle of Guimarães — #636 of 9,079 worldwide — 1 km north. The oldest dated site in the circle is Citânia de Sanfins, founded c. 450 BC.
The 100 km circle reaches into 2 countries — Portugal (39), Spain (9).