The land around Poole Harbour is flat, green and unusually accessible, which makes it good for the kind of day that involves walking boots or a bike rather than a ticket queue.
On foot
The shoreline path from Baiter round to Hamworthy follows the water for most of its length. Upton Country Park adds parkland and harbour frontage. The chines at Branksome and Canford Cliffs cut down through wooded valleys to the beach, which makes for a short, satisfying walk with a swim at the end. See walking and trails.
On two wheels
The cycling routes around the harbour are mostly level. Take the chain ferry from Sandbanks and you are in the Purbeck lanes within minutes.
Wildlife
Poole Harbour is a Site of Special Scientific Interest and a RAMSAR wetland, which means birds in numbers: waders on the mudflats, ospreys on passage, avocets through winter. Wildlife activities covers where to see what, and when.
For something gentler, see health and wellbeing.