Much like John Wemmick himself, Walworth is diminutive, but mighty. When Pip walks home with Wemmick, he is surprised. Wemmick's house was a little wooden cottage in the middle of garden plots with the top of it "cut out and painted like a battery mounted with guns." Since a battery is a fortification equipped with artillery, the top of his little house looks like a fortress. Wemmick also has a large flag on a pole, and he runs up a real flag. In addition, there is a little moat with a miniature drawbridge for his castle/cottage. The bridge is only a plank and the "moat" is but four feet wide and two feet deep. At nine o'clock Greenwich (official) time, the miniature cannon is fired; Wemmick has named this mighty gun "Stinger." The cannon is mounted is a separate structure, a "fortress" made of latticework. A little tarpaulin protects the gun much like an unbrella. All of these constructions have been fashioned by Wemmick, who calls himself his "own Jack-of-all-trades."
Provisions for his fortress are provided by a pig, fowls, rabbits, cucumbers and other vegetables. Wemmick takes great pride in his little world that pleases his Aged Parent and brushes away "the cobwebs" of Little Britain.
You should probably draw a big castle with lots of trees and tall structures.