We visited the cathedral and museum today.   The mosaic covered inside is incredibly decorated,  but without a lot of sunlight appeared dark.  Gold leaf was baked onto the glass to make the background gold! The museum has remnants of some older mosaics we could view up closed as well as the original bronze horses, which could be as old as 2100 years. Enjoy our photos at https://susandemaggio.smugmug.com/St-Marks-Basilica–VENICE