Thanks so much to Malo Mystery who provided the following additional information:
"The old Town House (Dorphuis) is a building on Greenmarket Square that was built in 1761 and was one of the city's first double storey buildings. It has been used as the seat for the Burgher (citizen) Senate, a magistrate's court, a police station and as the City Hall until 1905 when the next City Hall was completed. In 1916 it became the city's first art museum and is still used to house art and as a venue for musical performances."
This is an easy park n grab. It's a magnetic nano. There is parking in the shopping centre lot behind the GZ. This parking lot closes late evening and re-opens at 08:15 in the morning. Else one can park temporarily right next to the GZ. The cache is accessible without entering the parking lot.