Pre-cruise: we walked to The White Cliffs of Dover (about a mile from our hotel to visitor center), and walked aaaalll the way east to the National Trust Lighthouse (another 2 mile hike from visitor center to the Lighthouse). It’s a beautiful walk with gorgeous views and I highly recommend it if anyone there who has at least 2-3 hours in Dover.
B2B day: We took a taxi from the cruise terminal to Dover Castle, enjoyed about 4 hours or so there, then walked back to the ship, and with our Transit Express Cards we bypasses any lines that was there, went directly to the security xray, then straight onto the ship with our new S&S cards on hand.