The hook
France's eating city, built where two rivers meet, with a Renaissance old town threaded by traboules — covered passages cut straight through the middle of buildings, unmarked, that let you walk from one street to the next through somebody's courtyard.
01Why it's worth it
Lyon is the counter-argument to spending a whole French trip in Paris, and it is a strong one.
The traboules are the thing that exists nowhere else at this scale. Silk workers in Vieux Lyon and on the Croix-Rousse hill needed to carry bolts of cloth downhill without getting them wet, so the buildings were built through — a few hundred passages linking parallel streets, up staircases and across courtyards. Most are private now, but dozens are open to walk, marked by a small plaque or nothing at all. The Resistance used them during the occupation for exactly the reason they are disorienting: someone who does not know the network cannot follow you through it.
The food is the other reason people come. Lyon's bouchons are small, loud, and unbothered — quenelles, pike dumplings in crayfish sauce, andouillette for the brave, and lyonnaise salad — and the city has kept a price level that Paris has not. A proper two- or three-course lunch here still costs less than a mediocre one elsewhere.
Above the old town, Fourvière hill carries a basilica and, behind it, two Roman theatres still used for summer concerts, because this was Lugdunum, capital of Roman Gaul. The funicular that climbs to it is ordinary public transport, not an attraction with an attraction's pricing. Below, the two rivers — Rhône and Saône — have long walkable banks that fill on summer evenings.
02How to experience it
Two days. Walk Vieux Lyon in the morning with a traboule map and let yourself get lost in the passages; take the funicular up to Fourvière for the view and the Roman theatres; eat lunch in a bouchon rather than dinner, when the menus are cheapest. Cross to the Croix-Rousse for the silk-workers' quarter and the steeper, quieter traboules. Spend an evening on the Rhône bank.
From the locals
The recommendation in the r/travel France thread comes from someone who lived there and does not hedge: "I lived in the city of Lyon for a time and could not recommend visiting it higher."
Their specifics are the plan above, more or less: "if you're a foodie, it's heaven — you can have some pretty awesome 2 or 3 course meals for 15–20 euros a head. The cathedral on the top of the hill can only be accessed by a funicular ride uphill that's great fun (and part of the local infrastructure, so no weird novelty charges) and gives beautiful views over the city. Walking along the banks of the two rivers is a lovely way to spend an evening. Old town is really cobblestoned and pretty, and good fun for a history geek to walk down the secret tunnels of the resistance army during WW2."
The same thread carries the wider point that makes Lyon worth the detour, from someone answering a traveller who had queued all week in Paris: "every single thing you listed was very touristy, so I'm not surprised you experienced queues… Paris is more about the atmosphere and the neighbourhoods, not about ticking off overrun sights."