We thoroughly enjoyed our time on Ortygia and at Casa Santo. The location is in the old Jewish quarter, on a interesting, narrow street - - near to the Duomo and to almost anything of interest on the island.
We loved the two terraces - - one on each floor- - which overlook an interesting roofscape and sunrise over the sea.
We appreciated the arrival (they arranged for a taxi from Catania airport - - ask for Pepe, the driver) including fruit and a bottle of Sicilian wine waiting for us on the kitchen table.
Good, well-equipped kitchen; clothes washer.
We were two couples, and one bedroom is clearly more desirable than the other - - but we worked that out.
A word of caution: access to the apartment is via a steep, outside stair. It was not a problem for us, but might be a problem for someone.
Overall- a great place to stay.