Things about Poole that are worth knowing, and a couple that are worth being sceptical about.
The harbour
Roughly 36 square kilometres at high water, and mostly under two metres deep. The "second largest natural harbour in the world" claim gets repeated a lot locally; it depends entirely on your definition, so treat it as a good pub line rather than a fact. See the harbour guide.
The boat in the museum
The Poole Logboat is around 2,300 years old, hollowed from a single oak, and was pulled from the harbour mud. It is one of the largest Iron Age logboats found in Britain. See museums and galleries.
The island that started Scouting
Baden-Powell's 1907 camp on Brownsea Island is treated as the beginning of Scouting worldwide. The island also kept its red squirrels when most of England lost theirs, because water is a good barrier.
The expensive sand
Sandbanks turns up regularly in lists of the world's priciest land. It is a sand spit about half a mile long with no room to build.
The cod money
The Georgian houses in the Old Town were paid for by salt cod. Poole merchants ran the Newfoundland fisheries for well over a century. See the history of Poole.