Day trip to Boulogne - what do I need to know?

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Haven't been for years , I remember the huge supermarket , going on the ferry < seasick , wandering about.
The three hour lunch breaks

We're going on a trip , via the tunnel so yay no driving .

Is there one main supermarket?
Where is nice to wander , some small shops .
Anywhere we should avoid ?

TIA

Since the ferry companies stopped running regular services, there's not a lot there anymore. It's a shame as Boulogne is a lovely town.

The sea front isn't much, but take the time to walk up into the citadel where the basilica and the old town is. You may still find some nice bistros for lunch.

The main supermarket is not near the town centre at all. It's a shame you won't have a car as the Cite Europe right by the tunnel has a huge Carrefour which is excellent.