Narbonne has been an ideal place to stop off when going places since Roman times as it was where the via Aquitania from the Atlantic via Bordeaux and Toulouse met the via Domitia reaching into Spain. It’s still a great place to change trains when doing the same thing.
Highlights
Medieval Archbishop's palace and cathedral
Roman Horreum
Narbo via exhibition
Station stroll ideas
If you have an hour or two to spare waiting for a train, why not go for a wander?
I've made a downloadable PDF and accompanying google map which will give you a feel for the place and take in the sights.
Luggage
If you want to stroll without a care in the world, including your luggage, you could try using the nannybag app to find a place that will take your bags.
Getting there
It takes around 30 mins from Carcassonne and around an hour and a half from Nîmes or Toulouse.
Useful links
Tourist info: https://www.cotedumidi.com/en/unmissable-narbonne/
Where next?
How about Carcassonne, Portbou or Figueres?