In Hungary in the sixties-seventies it was as easy as it could get. My grandmother actually traveled to St. Petersburg (not called that at the time) from Hungary. You needed a passport but there were no limitations on eastern travel (even in the eighties you could only travel to the west every third year) and the state-owned travel agency organised tours to the Soviet Union. You simply had to pay for the trip in Forints at home and they took you to a tour in the desired location.