Some change in scenery and some difference between what you leave to what you find. slowmoves offers an intimate means of experiencing this. Of course time does not allow us to make such a journey regularly, which is a reason in itself for treasuring the possibility, as is the more practical consideration of a night's accommodation included in the ride, if leaving as below:
1404: London St Pancras to Paris Gare du Nord (1726) - Train
1945: Paris Gare d'Austerlitz to Madrid (0910) - Train
1505: Madrid to Algeciras (2033) - Train
2100: Algeciras to Tarifa (2145) - Bush
2300: Tarifa to Tangier (2235: 35 minute crossing and time change) - Boat
Of course, there's the option of spending more time in Paris or Madrid or Algeciras, depending what your scheduled, motivation or interest is.
Thanks to The Man in Seat Sixty-One for helping with the travel information and image. The relevant Seat Sixty-On page also tells you how you can travel on from Tangier, and how the cost of travel drops.
This justification of experience, is at the heart of many slowmoves choices. I for one think it's well worth it.