If you plan to travel between the UK and mainland Europe, I highly recommend the ferry across the Channel. Although the Channel Tunnel Train can be exciting, you miss out on the stunning views above.
I caught an overnight ferry from Calais to Dover, and let me tell you, watching the sunrise at 4am over the White Cliffs of Dover was a surreal experience - not something to be missed.
Ferries can easily be booked online via the P&O Ferries site. Crossings are made multiple times a day and take approximately an hour and a half.