The Observatory has a tall tower attached with a telescope platform at the top. As printed in the book, the main body of the tower is a simple cylinder with a dark helical stripe. This stripe turns out on close inspection to be the representation of an open spiral staircase leading to an entry door near the top.
Considering the quality of the rest of the model, I considered it a pity that this staircase was not modelled fully, so decided to try doing so. Since I do not have a CAD program or draughting skill, but am comfortable writing computer programs for geometric modelling and graphics, this is what I did. All the shapes are calculated from the dimensions of the original artwork, so barring the expected silly mistakes the fit should be good first time.
The first thing was to construct a white outline version.
Everything fitted OK, except for the edging for the "ceiling" over the steps, which I miscalculated. Soon fixed, though. At this stage I also added parts for the interior of the opening a little less than half-way up, which reveals the internal wall and the start of another staircase.
Next came painting the various parts, using GIMP. For this I simply stole other bits of the model. Obviously the outer wall comes from the original outer wall artwork, but most of the rest came from the Tower of Art. Internal stonework is from the first stage of the Tower of Art, scaled more suitably, and the steps come from the entrance stairway, separated into individual steps and rotated to the correct angles.
The final build gave few problems, though at times three hands would have been useful.
I think that it is an improvement.
The complete Observatory.
I hope to make the pages available for others to play. Since the painting uses copyright material, though, I shall have to seek permission to do so first. For the time being here are the white patterns, as 300dpi PNG files, which you can use freely to paint yourself. The files are not huge - less than 100Kb each. There are (and probably will be) no instructions except for the photos above.