Bute Park runs along the River Taff from the castle to Llandaff in the north, 130 acres of landscaped gardens, mature arboretum, and riverbank path. The park was the private grounds of Cardiff Castle before it was given to the city in 1947, and the quality of the planting, specimen trees, formal garden sections, kitchen garden areas, reflects the original investment.
The walk along the Taff to Pontcanna Fields and beyond makes one of the best urban green corridors in Wales. Free, open all year, and one of Cardiff's most straightforwardly pleasant afternoons.