Calais (Dutch: Kales) is a city in the Nord-Pas de Calais region of France. It is the closest point on the French mainland to England; Dover lies across the English Channel (La Manche) just 32 km away. The town has a major cross-Channel ferry port, and the French entrance to the Channel Tunnel is nearby.
Calais is very popular with British day-trippers arriving by ferry or on Channel Tunnel shuttle trains: one reason being due to the fact that France has lower taxes on alcohol and tobacco than the UK. Large warehouse supermarkets have sprung up on the outskirts of Calais just to serve these British "booze cruisers" who return to the UK with their car suspensions groaning under the weight of cheap alcohol and cigarettes. While most tourists view the town as simply a port where one can buy cheap alcohol, cigarettes and groceries, there is more than that.
Calais is connected to Dover in England by ferry services operated by P&O Ferries , DFDS Seaways  and MyFerryLink . Ferry crossings between Dover and Calais take typically around 1 hour 30 mins and, combined between the operators, there are up to 41 sailings daily. The check-in time is 30 minutes before departure for vehicles and 45 minutes before departure for foot passengers.
The Strait of Dover is one of the most frequented shipping lanes in the world. The Calais ferry port allows easy access to the town itself as well as shops outside the town, many of which exist solely to sell alcohol to visitors from the UK.
Free car parking facilities are available in front of the Calais ferry terminal and the maximum stay is three days.
Another popular ferry route is Dover to Dunkirk (near Calais) which is operated by DFDS Seaways and takes around 2 hours. This route is popular due to the fact that the nearby town of Adinkerke (in Belgium) has lower taxes on tobacco than both France and the UK, thus British day-trippers have convenient access to both cheap tobacco and alcohol rather than just the latter via this ferry route.
Passengers travelling by ferry from Dover to Calais/Dunkirk go through French passport/identity card checks in the UK before embarkation, rather than on arrival in France. Passengers travelling in the other direction from Calais/Dunkirk to Dover by ferry go through French exit checks and UK passport/identity card checks in Calais/Dunkirk before embarkation, and UK customs checks on arrival in the UK.
Fares for the Dover-Calais ferry vary heavily, depending on which company you book with and when you travel. As a typical example, if booked online, P&O charge £35 for a single, £28 for a 3-day return and £45 for a 5-day return for a car and up to 9 passengers.
Note that Calais Fréthun station is some distance from Calais city centre, but there are a number of trains operating between Calais Fréthun and Calais Ville (in the city centre), as well as shuttle buses and taxis.
The Eurostar timetable is available from their website .
Passengers travelling by Eurostar from the UK to Calais go through French passport/identity card checks in the UK before boarding the train, rather than on arrival in France. Passengers travelling in the other direction from Calais to the UK by Eurostar go through French exit checks, followed by UK passport/identity card checks in Calais Fréthun station before boarding the train, and UK customs checks on arrival in the UK.
Those travelling by Eurostar between Brussels and Calais are within the Schengen Area, however passengers are still subject to UK immigration controls.
Although the Brussels Midi-Calais Fréthun route can't be purchased through the Eurostar website, it is available on the Belgian Railways website .
Eurostar fares start from £66 return (under 26) and £69 return (adults) from the UK to Calais .
Eurotunnel (Le Shuttle)
Running from Folkestone to the western edge of Calais (Coquelles), this car shuttle service operated by Eurotunnel  takes about 35 min (although only about 20 min of the journey is in the tunnel) and offers the fastest way to travel between the UK and Calais. This train service is for passengers with cars only, who remain with their car for the duration of the short trip. There are toilet facilities onboard.
Passengers travelling from Folkestone to Calais go through French passport/identity card checks in the UK before boarding the train, rather than on arrival in France. Those travelling in the other direction from Calais to the UK by Eurotunnel go through UK passport/identity card and customs checks in Coquelles before boarding the train, rather than on arrival in the UK.
Running from Lille, Boulogne, Dunkirk and Paris, Calais is well supported by the French national rail network. Calais Ville is the station serving the city centre, whilst Calais Fréthun is located on the outskirts of Calais. There are trains that operate between Calais Ville and Calais Fréthun stations.
The Motorail service linking Calais with Narbonne, Marseille and Lyon was withdrawn in 2010 owing to rising costs & poor exchange rates.
Calais is directly linked to the French autoroute system. The two autoroutes that serve Calais are the A26/E15 (Autoroute des Anglais), which provides access to the heart of France (including Paris and beyond) and the A16/E40, a gateway to the Benelux and the northern European motorway systems. The A16/E402 also directs you to western France, including Boulogne.
Eurolines  operate daily buses from Paris, Lyon and London to Calais. Some services from London also stop at/near Gillingham, Canterbury, Folkestone and/or Dover en route. The Eurolines stop in Calais varies - services which operate across the Channel via the tunnel stop at the Cite Europe shopping centre, whereas the services which use the ferry stop at the ferry terminal.
Megabus  operate buses from Paris, London and Birmingham to nearby Boulogne, with through fares available from the company's network in the UK. Despite the fact that Megabus services use the ferry from Dover to Calais, they do not stop in Calais itself; hence if one is travelling from the UK it makes more sense to travel by other means.
Most people travel by car around the town, but there is a comprehensive network of buses running from the town centre to the suburbs and Cité Europe. The port is served by a special shuttle bus although via a footbridge the centre, and the harbour terminal are only 15 min apart.
Bus 5 is useful for reaching the large Auchan and Carrefour hypermarkets and the Cite Europe shopping mall and the 6 goes to Calais Frethun Eurostar station. Services run every 30 min during the day and costs about €1 (board through the front door and pay the driver) and all buses terminate outside the Gare D'Ville.
As is the case in the rest of France (and most of Europe), the sole official currency is the euro (EUR, €). However, many shops frequented by tourists (particularly the alcohol-selling warehouse supermarkets on the outskirts of the city) also accept the pound sterling (GBP, £).
For a lot more infos, have a look on the Couchsurfing Wiki Page of Calais. 
To hitchhike to Belgium or the Netherlands, if you leave the terminal, you must walk 500 m through a large car park, after which you will see roundabout and an on-ramp to the motorway. That is the place to hitch a ride: there is enough space even for a big lorry.
For a more 'traditional' experience of France, Saint-Omer is a mere 26 miles (43 kilometres) down the road from Calais. The Saturday morning market on the main square, the Place Foch, can be enjoyable. There are also good affordable restaurants and friendly bars, as well as interesting architecture.