The closest is Geeraard de Duivelsteen, 1 km south-east of the city centre; the most famous is Royal Palace of Brussels — #226 of 8,133 worldwide — 50 km south-east. The oldest dated site in the circle is Bornem Castle, founded c. 1000.
The 100 km circle reaches into 3 countries — Belgium (48), Netherlands (12), France (6).