Restarting the Navitor: See Cornelius's sketch and go from Spring to Winter.
The puzzle: Rebuild, and add your own touch.
1. Restart the Navitor.
On Kal. Nov., it becomes Winter. This one is complex; there's a sketch of part of it in one of Cornelius's scrolls. Again, at the double doors, get the note with the number code (41); go to the Hiems table at the left of the Navitor, enter XLI, get the piece, attach it next to the similar piece on the right of the machine, run the machine by clicking on the handle and holding down the mouse button, and pull the knob. Then go through the Ver door to find the Hiems door at the left and the final machine. Each of the three levers has three positions; the big one on the left (marked A in Cornelius's drawing) goes from left to right, I II III; the next (B and C) go from down to up, I II III. Put A at II, B at III, and C at II. Then press the button (D) and WORK QUICKLY: B at II, C at III, B at I, A at I. If the machine dies down before you complete the second sequence, just start over. When it's running, go back to the Navitor.
2. Gordian's Temple/Arch (a.d. XVI Kal. Dec.)
You'll see references in the scrolls and Acta to the building and destruction of Gordian's temple. Go to the building site (south of Saturn, near where you entered the Tiber area). You'll see a toppled arch and a crane with a lever. Rebuild the archway by clicking on a piece to get the crane to pick it up, rotating the piece with the lever, and clicking on where you want it to go. Start with a rectangle at the bottom left space, a square at the bottom right, a rectangle to the left, a square to the left, a rectangle to the left, a rectangle with a curve on its right side to the left, and a rectangle with a curve on its left side to the right. Then get the big wooden arch piece, rotate so that the straight side is on the bottom, and put the piece on the top. Then add the small arch piece, rotate it, and place on the right side. Click on the arch form you got from the September puzzle and put it on top. Then add the small curved pieces and, finally, the keystone. When it transforms into a completed archway, click on the top of it to go through into the building site. Among the rubble, find the axe, a wooden soldier, and a scroll. You'll notice when you look up that a wall has opened just beyond this area; this is the Elements Door, but don't try to solve that one until you've completed December's puzzle and are ready to proceed to the endgame.