Options for P&O Ferry foot passengers, traveling from Calais to Dover - rather than the other way round. There is also always the option of a taxi from the train station, but if you want a little more adventure, this is what we did (twice):
Trains arrive at Calais Ville or Calais Frethun. If arrive at Calais Frethun, there are connections. For a schedule, follow the links on the Ville De Calais webpage: http://www.calais.fr/. If you have almost no French language skills (like me) you can follow the menu items from the main page, as it appears that only the main homepage can translate to English:
Accueil > Vie quotidienne > Se déplacer > Navettes des gares Lille Europe <-> Calais-Ville <-> Calais Fréthun
From the Calais Ville train station, you have two options. (There is also always the option of a taxi, but we were a group of five with too much luggage and didn’t want to take two taxis, this is what we did):
There is a ferry shuttle bus that runs from the station to the P&O Ferry terminal (disclaimer: I have never used this, and I have no idea if there is a fee for this). There are two bus shelters around the corner from the train station - out the main station doors, turn left onto the Quai du Rhin, and it is just about 20 feet back to the left and across the street, along a big parking lot. The ferry shuttle schedule is mounted in it’s bus shelter, and sadly was never convenient for our use. Earliest run was at 10:45 am, and we were there hours earlier.
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The Balad’in bus and walking. This is a free bus in the downtown. It runs from the Jardin des Plante to the Matelote, approximately every 15 minutes. It is easy to catch - there is a stop right across the street (Boulevard Jacquard) from the Calais Ville station. The stop is not the bus shelter - there is a funny little yellow and blue sign just next to the shelter. Be warned that these are tiny little buses - they maybe hold 10 people, unless the people are very friendly. The stop closest to the ferry terminal is the C.C.I. stop. Ding the bell on the bus after you see the big grey lighthouse (le Phare de Calais), and you will be close enough. There is a schedule and map (plan) here: http://www.sitac-calais-opale-bus.fr/index.php/nos-offres-de-transport/balad-in
From the C.C.I. stop, it is about 2 km walk to the terminal. There are two ramp sections, and the first part has no curb cuts. Most of the walk is cobbles. I say this because it can be a hassle with heavy luggage (even the wheeled kind). My slightly overpacked parents struggled a bit, but they managed it (they are reasonably fit, and in their late-70s). Give yourselves a half-hour, and you should be fine. The route: (this is simplest on the left side of the street, facing oncoming traffic). Walk east (toward the lighthouse) on the Boulevard des Allies. The road curves - keep following along the road with the tracks. When the tracks cross and leave the road, keep straight along the road, keeping the tracks to your left. At the T intersection (with Pont Vetillard), turn left onto Pont Vetillard. Cross the tracks, and continue along Pont Vetillard and over a lock. Keep along - you will arrive at a roundabout. Cross the crosswalk on the first arm of the roundabout, and keep along the left sidewalk of the second arm (Avenue du Commandant Cousteau). The first arm of the roundabout (an off-ramp from the ferry docks) has no sidewalk, so it shouldn’t be as confusing in real life as it sounds here. Just past the roundabout along the Avenue du Commandant Cousteau, you will see a blue sign on your left and a ramp for foot passengers to get to the terminal. Follow it up and over the car loading areas and down the other side, and there you are. Once you are on the ramp, there are no places to deviate from the route.