"Later, I looked up the Bornholmer Bridge on a street map. I had heard of it, and thought it might have been one of the places East and West Germany used to exchange each other's spies."

Map of the Bornholmer Strasse checkpoint:

Google Map

When the loosening of travel restrictions from the GDR was announced on 9 November 1989, the Bornholmer Strasse checkpoint was flooded with hoards of people trying to pass through to the west; some wanted to escape forever, others wanted to go for a couple of hours to have a look around... just because they could. There's more about this on page 182 and some incredible footage on the Bookmark for that page.