First, the Forbidden City, Jingshan Park and Beihai Park were built into drawers according to the situation that everyone should visit one place or at most two places, and then 1987 campers were put into the drawers, which solved the problem.

Solution: Because campers can go to six places: (Forbidden City), (Jingshan), (Beihai), (Forbidden City, Beihai), (Forbidden City, Jingshan), (Beihai, Jingshan) and * * *.

The structure is 6 drawers with 1987 campers.

According to the pigeon hole principle, there must be 1987÷6+ 1=332 people visiting the same place.