Seven days, seven distinct ideas, none of which repeat the one before.
Day 1: the Quay and the Old Town
Start where the town did. Poole Museum is free and holds the Iron Age logboat; the Cockle Trail links the Georgian merchant streets behind it in ninety minutes. Dinner on the water. See Poole Quay.
Day 2: Brownsea Island
Twenty minutes by boat. Red squirrels in the pines, peacocks on the paths, and a lagoon with hides over one of the best bird sites on the south coast. Allow three to four hours. See Brownsea Island.
Day 3: a beach, properly
Sandbanks if you want facilities and lifeguards, Branksome Dene if you want quiet, Hamworthy Park if you have small children. Arrive early for parking.
Day 4: across the water
Chain ferry to Studland, then the coast path to Old Harry Rocks, where the Jurassic Coast begins. A mile and a half each way.
Day 5: on the water
A sailing or paddleboarding lesson in the sheltered harbour, or a harbour cruise if you would rather be a passenger. See watersports.
Day 6: the hills
Corfe Castle and the Purbeck ridge, with the Swanage Railway running steam through the village. See Dorset and countryside.
Day 7: inland
Wimborne Minster for the twin-towered church and the chained library, then Compton Acres on the way back for the gardens and a tea room.
Where to stay for all of this: accommodation.