Photo: Ra-smit at Dutch Wikipedia, CC BY-SA 3.0 Free historic sites in Groningen
Photo: Ra-smit at Dutch Wikipedia, CC BY-SA 3.0 Grote Markt
Free, always
Photo: Gouwenaar, Public domain Der Aa-kerk
Free outside, paid inside
Photo: nl:Gebruiker:Ra-smit, colour adapted by User:Lyzzy, CC BY-SA 3.0