Antwerp coalhole covers?

After my disappointing (coalhole cover-wise) trip to France, I wasn't expecting much from a long weekend in the rather wonderful city of Antwerp. After wandering the streets, bars and museums of Antwerp, idly keeping an eye out for interesting person-holes, I noticed that many of the old buildings had semi-circular grilles in front of their doorsteps.

Peering down these holes, I couldn't see any window or other indication that these were to give light or ventilation to basements - indeed many buildings also had rectangular lightwells. Many of the grilles had chains attaching them to something in the abyss below.

Given Belguim used to have a vibrant coal industry, I assume these are examples of Belgian coalhole covers - possibly the first pictured on the interweb!

In a lovely modern Museum Aan de Stroom, I also found these intriguing medallions set into the floor slabs, designed by Tom Hautekiet, based on the plans for Palmanova, the ideal Renaissance city. They would make ideal coalhole cover designs.

 
  Other places I visited in Antwerp are reviewed here, but not the excellent bars.