St Ives leisure centre
Its raining: the pasties are taking the toll; the full Cornish breakfasts are making you feel guilty; the kids want a muck about - whatever the excuse you could pop up to St Ives Leisure Centre and tone up with a swim in the 30m pool or, if so inclined workout at the Harpers fitness suite (with great views over the Bay).
You can walk from the hotel, about 15 minutes uphill (really uphill and a workout in itself!) and then you have the easy walk down.
