In 1946, Dag Hammarskjöld popularised the expression ""vår sista stora vildmark"" ("our last great wilderness"). Dag Hammarskjöld advocated a growing tourism in the park, that took care not to damage the environment. Edvin Nilsson's 1970 book on the park strengthened its reputation, increasing the number of tourists from two or three hundred in the 1960s, to 2,000 in 1971. This sudden success caused several problems such as the temporary overcrowding on certain trails in the Rapa Valley, which were not designed to accommodate so many visitors.