Patrick gave me this children's building toy. He got them cheap at a discount store and had used a set to build a tower house for his Scottish boarder game.
The bricks are enormous for 20mm figures, so I used a needle file to inscribe more stone lines into the faces. Although when it came to painting I hadn't gone deep enough and had to be careful not to paint the cracks out.
So four bricks for each well, inscribed with a rough brick pattern, glued to a base and painted. I then used some dry static grass to soften the bottom edge.