Start from the museum end of the car park, picking up the riverside trail and following a wide loop of the River Arun to reach the wetland centre (paid entry), home to glow worms, bee orchids, bats, warblers and rare blue ducks. Bear left, away from the river, tracing the edge of the wetlands and crossing the road to reach Swanbourne Lake. Follow the footpath around the lake, its clear chalk-bed water offering a window into the world below. Return alongside the road below the towers and turrets of Arundel Castle, the oldest part of which – the motte, a grassy artificial mound – dates to 1068. Tarrant Street Espresso, a few minutes’ walk from the start, serves a restorative flat white and brownies.