Question: When did they visit parking?
SQL: SELECT  T3.visit_date FROM Tourist_Attractions AS T1 JOIN VISITORS AS T2 JOIN VISITS AS T3 ON T1.Tourist_Attraction_ID   =   T3.Tourist_Attraction_ID AND T2.Tourist_ID   =   T3.Tourist_ID WHERE T2.Tourist_Details   =   "Vincent" union SELECT  T3.VISIT_DATE FROM Tourist_Attractions AS T1 JOIN VISITORS AS T2 JOIN VISITS AS T3 ON T1.Tourist_Attraction_ID   =   T3.Tourist_Attraction_ID AND T2.Tourist_ID   =   T3.Tourist_ID WHERE T2.Tourist_Details   =   "Marcelle"