Start at Falmouth Market in the town centre, ideally around 9:30am, when the stalls are lively but not yet picked over. Browse Cornish baked goods, local produce and small crafts, then wander along Market Strand and the compact streets around Church Street. The market is usually held on selected days rather than daily, so check the current schedule before setting out; if it is not running, use the time for a relaxed coffee and town-centre wander instead. Allow about an hour, then walk downhill towards Discovery Quay—roughly 10–15 minutes—to the National Maritime Museum Cornwall. Give the museum around two hours for its hands-on galleries, boats and harbour-facing exhibits; adult admission is typically about £16–20, with tickets often valid for repeat visits.
For lunch, stay by Falmouth Harbour and choose a seafood restaurant or café along Custom House Quay or the nearby waterfront. Fresh fish, mussels, crab and Cornish specialities are the natural choices, with lunch generally costing £20–35 per person before drinks. Book ahead if you want a specific table, particularly on a September Thursday, though the harbour is also good for simply choosing somewhere that suits your pace. From the waterfront, take a taxi to Pendennis Castle—about 15 minutes, depending on traffic—or walk in roughly 30 minutes via Castle Drive if you would rather make the approach on foot.
Spend around two hours at Pendennis Castle, one of Henry VIII’s coastal fortresses, exploring the Tudor defences, later military buildings and broad views across Falmouth Bay. September opening hours commonly run through the afternoon, but check the exact closing time and admission price before leaving; adult entry is usually around £15–25, with online tickets sometimes cheaper. Afterwards, walk or take a short taxi ride to Gyllyngvase Beach. A gentle stroll along the sand and seafront is worthwhile even if the water is too cool for swimming; check the tide and conditions, and remember that the beach facilities and café may close earlier outside peak summer. Return towards the harbour for dinner at The Wheel House on Custom House Quay, a popular informal seafood spot where £25–40 per person is a realistic budget. Reserve ahead where possible, as it is small and can fill quickly; after dinner, the harbour is lovely for a final lantern-lit stroll.