Take the Eurostar from London St Pancras International to Paris Gare du Nord this evening — it’s the easiest, most civilized way to cross the Channel, with a journey time of about 2h20. I’d aim to arrive at St Pancras 60–90 minutes early so you have time for security and border control without rushing; if you’ve got checked luggage, keep it light, because the whole point of Eurostar is to glide in, not drag a suitcase parade through stations. Once you roll into Gare du Nord, you’re already in the city, and from there it’s a simple Métro hop or a short taxi into the 10th arrondissement.
For your first stretch on the ground, do a relaxed Canal Saint-Martin stroll. This is the kind of Paris locals actually come to unwind in: iron footbridges, tree-lined water, cafés spilling onto the pavement, and just enough buzz to make you feel like you’ve arrived without throwing you straight into sightseeing mode. If you want a quick beverage or a snack before dinner, the canal edge around Rue de Lancry and Quai de Jemmapes is especially pleasant in the evening. Expect an easy hour here, and don’t over-plan it — this is more about settling into the city than checking off boxes.
Head to Breizh Café for dinner; it’s a very reliable choice if you want excellent galettes, proper Breton cider, and a place that feels casual but still special. It’s a good first-night dinner because you can eat well without committing to a long, formal meal — figure roughly €20–35 per person depending on what you order. Afterward, if you still have energy, wander over toward the Le Comptoir Général area for a final drink or dessert vibe; even if you don’t go in, the surrounding canal-side streets are nice for a slow evening walk. Then make your way back by Paris Métro or taxi, depending on how late it is and where you’re staying — from the canal area, allow 20–40 minutes and try to head off before the night gets too long, so you actually enjoy tomorrow instead of recovering from it.