My one ferry trip to Calais was also my first venture abroad. It was 1967 and my parents and I took the SR-N6 hovercraft from Ramsgate on a day trip. Back then you could do things like this without a proper passport.
Once on French soil we wandered the town, I ordered some wine for us in my high-school French and we bought a few pastries—I remember little other than the town hall! We took several photos of ferries arriving and leaving, but not one of the hovercraft that we used. (See the Ramsgate and Pegwell Bay ferries page for more about the hovercraft services.)
At its narrowest, the Channel is only 21 miles wide, and Calais and Dover are barely any further apart than that. So Calais has always been the most popular Continental port of entry when coming from Britain—in fact from 1347 to 1558 it was an English possession and a major trade hub.
At its peak there were boat ferries from Calais to Dover and Folkestone and hovercraft to Ramsgate. Now Dover remains the only destination for ferries, although 10 million people a year use the Channel Tunnel whose termini are at Calais and Folkestone.
I've since passed through Calais a couple more times, in 1999 and 2009, but on these occasions it was heading to and from the Channel Tunnel. The Tunnel is fun to use once or twice, but never gives the same feel as being on a ferry for an hour or two, enjoying the wind and watching one coast recede as the other approaches. It's unfortunate that over the past few years Calais has hit the news mainly as an assembly point for potential illegal immigrants into Britain.