Bute Park begins almost at the back door of Cardiff Castle and then opens into a long, generous sweep of lawns, tree collections and riverside paths. It is not just a patch of grass in the centre: the park carries the scale of the old castle grounds, with enough room to make the city feel suddenly less busy a few minutes after leaving the shopping streets.
Use it as a slow route rather than a box to tick. You can walk north beside the River Taff, look for the arboretum plantings, or loop back toward the civic centre and Cathays Park. In good weather it is one of Cardiff's best places to pause, especially if the castle and museums have made the day feel a little heavy indoors.