This somber yet soaring church is one of Thessaloniki’s oldest and most important. Look up and admire the artistic talent of the creators of ancient mosaics, delight in the dazzling icons, ponder the mystery of the faded frescos and revel in the grandeur of the gold chandeliers. Also make sure to check out the shiny, elaborately decorated casket in one of the side chapels.. From the looks of it, there’s got to be someone pretty important in there.