The graceful lines of the rectangular choir and 16-sided cupola are best viewed from the little cloister that he built on the north side.
You are unable to see the cloister from the north side. 
mnli hypothesis: You are unable to see the cloister from the north side.  premise: The graceful lines of the rectangular choir and 16-sided cupola are best viewed from the little cloister that he built on the north side.