The setting of Orvieto on the tuffa plateau is impresive. The cathedral with its simple interior and opulent facade is really masterpiece. Another pleasent place of Orvieto is Piazza dell Popolo (Palazzo del Popolo - PHOTO). My personal highlight is the Chapel of the Corporal with the stained corporal of the miracle of Bolsena - in fact it was the reason for the errection of the Cathedral.  

I think that one can spend wonderfull time enjoying the histrorical monuments, picturesque streets, excellent white wine and naturally excelent Italian food in Orvieto even without the WHS status.