I second the Botanical Garden - if the weather is good, take a picnic. Get your lunch ingredients including excellent wines, pate & cheeses from Marché des Capucins, it is about as French as you can get, one stall just sells fresh herbs - check out Rick Stein’s Bordeaux weekend. He also visited Entrecote.
The Quartier Saint Michel is the place to go for Cous-cous, all foods north African & wonderful mint tea.
I took the single track train out into Margaux & Pauillac - but to be honest would not bother going again - monoculture vineyards, empty villages (all gone on hiliday) eye-wateringly expensive restaurants. MUCH better is the village (small town?) of Cadillac which is much more genuine, heading out towards St Emillion.
Bordeaux in the evening is lovely, can be smelly, but I really loved it.