Calais is often overlooked by Brits passing through on their way to far-flung places, but they're missing out on some little gems and the odd dragon.
Rodin's burgers of Calais
If you have an hour or two to spare waiting for a train, why not go for a wander?
Tourist info provide a set of walks and hikes here.
I've also made a downloadable PDF and accompanying google map which will give you a feel for the place and take in the sights.
If you'd like a guided tour, Tourist info provide details here. They also offer a greeter service - locals who will show you around their town. You can find out more about it here
If you want to stroll without a care in the world, including your luggage, you could try using Bounce to find a place that will take your bags.
Ferry
Paris 3 hours
Lille 1 hour
Tourist info: https://www.calais-cotedopale.co.uk/
How about Boulogne or Lille?