The GR 120, also called the GR du Littoral, runs along the entire Opal Coast De Panne in Belgium to Berck Plage. The total distance of the walking route is 175 km. The route runs right through the most beautiful natural areas of the Opal Coast (Les Dunes du Peroquet and Les Dunes Marchand, Le Platier d'Oye, le Site des 2 Caps, les Dunes de la Slack), crosses the main cities (Dunkirk, Calais and Boulogne) and small coastal towns (Le Touquet, Wimereux, Audresselles, Ambleteuses, Wissant, Bray-Dunes).
The topoguide describing the route has disappeared from the trade, but the red-white signage is still OK. A road description is not really needed. If you lose the track, then walk again towards the coast and soon you will encounter the red-and-white characters again
You can download the GPX route from the GR120 . For those with no experience, there is a short guide. Did you know that you can use the GPX routes on most smartphones?
Below you can see an example of a GPX route in Garmin Basecamp, with the free OSM tickets.
On the pictures below, taken from the infoboards in the nature reserves, you see the GR120 as a red line.