[3] Instead of nestling on the valley floor like Morlaix, most urban development has been on the hillside overlooking the river Rance.

The Rance has moderate turbidity and its brownish water is somewhat low in velocity due to the very low gradient of the watercourse; pH levels have been measured at a slightly basic 8.13[4] within the city, and electrical conductivity of the waters has tested at 33 micro-siemens per centimetre.

In the centre of Dinan, the Rance's summer flows are typically low, in the range of 14 cubic metres per second (490 cu ft/s).

For many years, the bridge over the river Rance at Dinan was the most northerly crossing point on the river, but the tidal power station at the mouth of the estuary, constructed in the 1960s downstream from Dinan, incorporates a 750-metre long tidal barrage, which also serves as a crossing point nearer to the sea.

The town is transformed with decoration and many locals dress up in medieval garb for this two-day festival.