Seafest Plymouth

Plymouth's seafood-and-harbour festival spreads across the whole waterfront — the historic Barbican, Sutton Harbour, Tinside Lido and Royal William Yard all get a slice of it, with a working fish auction, crab-picking and lobster-pot-making demos, and a trail of sea-themed craft activities that keep younger kids busy without it feeling like a theme park.

It's free to wander, genuinely tied to Plymouth's fishing heritage rather than a generic food-festival format bolted onto a nice location, and big enough that you can dip in for an hour or make a full day of it along the harbour. Go for the free family trail and stay for the seafood stalls.