At first sight, Elsinor Castle, with its glass windows and sophisticated casements, was disappointingly modern, but as one walks through the portal one begins to feel the presence of history.
a)At first sight, Elsinor Castle, with its glass windows and sophisticated casements, was
seems correct!
b)At first sight, Elsinor Castle, which has glass windows and sophisticated casements, was
'have' seems strange!
c) At first sight, Elsinor Castle, with its glass windows and sophisticated casements, is
'is' wrong, we need a past tense
d)Elsinor Castle, with its glass windows and sophisticated casements at first sight is
'...at first sight is' awkward!
e)Elsinor Castle, at first sight, with its glass windows and sophisticated casements, are
'are' is wrong, since Elsinor Castle is singular