Ok. We purchased our voucher on line -cannot remember the name of the company so yours maybe different. We found it difficult to find our tour leader. If you face the Duomo and go down the road to the right about 100 yards there was a building where we met the leader and were given our ear phones. To us it was not obvious that this was the start point - maybe you will bet better directions. Suggest you get there early to be on the safe side as it will be manic. There was a service on when we went round and there was some restricted access but of no real concern. We had a great tour- a high light of our stay. PS you will get searched on the way in so the less you carry the better