Cardiff is actually pretty flat and actually quite compact as a city so easy to do some site seeing at the castle in the city centre, do some retail therapy around lunch in the many eateries and then either walk, cycle (on the many public bikes you can hire), hop on a frequent bus or catch a river ferry boat down the famous River Taff past the Millennium/Principality Stadium right down to the delightful Cardiff Bay. Here you can see a show or musical in the Copper-topped Millennium Centre, take a boat trip around the Bay, take a walk to the wetlands or the Cardiff Barrage, or simply put your feet up in one of the many cafes, bars or restaurants there and gaze at the beautiful view across the Bay. So much to see and do that one visit is never enough to this friendly city.