The closest is Racibórz Castle, 20 km west of the city centre; the most famous is Jasna Góra Monastery — #166 of 8,133 worldwide — 91 km north-east. The oldest dated site in the circle is Olsztyn Castle, founded c. 1201.
The 100 km circle reaches into 3 countries — Poland (49), Czech Republic (11), Slovakia (3).