Last year we did the 4 night pre-cruise in Moscow. Yes, we had to have a Russian visa. We got it through Zierer Visa Service (ZVS). You have to carry it with you at all times. We saw alot of people having their papers checked by the police. We did not; but did see alot of people getting checked in and around Red Square. Check with Radisson and see if it is required for a one day tour from St. Pete's. You probably won't need one if you stay with the group but do not wonder off in a store or anywhere else. It is well worth the trouble of getting one if necessary. You will really like Moscow. The Kremlin is worth the trip; especially the Armory!