I wanted to do a day trip in Wales, but am not sure which place I should visit. I plan on getting there early in the morning to return to London in the evening. I want to see a castle, cliffs by an ocean (hopefully a castle on a cliff by the beach!). I've been researching and places such as Swansea, Pembroke, Snowdonia, and the Great Orme looked like what I'm looking for, but there are probably a bunch I don't know about. In terms of transportation and time combined with just a day, which place in Wales would you recommend I visit? How would I get there from central London? Thanks in advance.